![Andi Kleen](/assets/img/avatar_default.png)
The mmio tracer sets io mapping PTEs and PMDs to non present when enabled without inverting the address bits, which makes the PTE entry vulnerable for L1TF. Make it use the right low level macros to actually invert the address bits to protect against L1TF. In principle this could be avoided because MMIO tracing is not likely to be enabled on production machines, but the fix is straigt forward and for consistency sake it's better to get rid of the open coded PTE manipulation. Signed-off-by: Andi Kleen <ak@linux.intel.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
628 lines
16 KiB
C
628 lines
16 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/* Support for MMIO probes.
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* Benfit many code from kprobes
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* (C) 2002 Louis Zhuang <louis.zhuang@intel.com>.
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* 2007 Alexander Eichner
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* 2008 Pekka Paalanen <pq@iki.fi>
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*/
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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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#include <linux/list.h>
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#include <linux/rculist.h>
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#include <linux/spinlock.h>
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#include <linux/hash.h>
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#include <linux/export.h>
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#include <linux/kernel.h>
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#include <linux/uaccess.h>
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#include <linux/ptrace.h>
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#include <linux/preempt.h>
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#include <linux/percpu.h>
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#include <linux/kdebug.h>
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#include <linux/mutex.h>
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#include <linux/io.h>
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#include <linux/slab.h>
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#include <asm/cacheflush.h>
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#include <asm/tlbflush.h>
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#include <linux/errno.h>
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#include <asm/debugreg.h>
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#include <linux/mmiotrace.h>
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#define KMMIO_PAGE_HASH_BITS 4
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#define KMMIO_PAGE_TABLE_SIZE (1 << KMMIO_PAGE_HASH_BITS)
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struct kmmio_fault_page {
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struct list_head list;
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struct kmmio_fault_page *release_next;
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unsigned long addr; /* the requested address */
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pteval_t old_presence; /* page presence prior to arming */
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bool armed;
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/*
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* Number of times this page has been registered as a part
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* of a probe. If zero, page is disarmed and this may be freed.
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* Used only by writers (RCU) and post_kmmio_handler().
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* Protected by kmmio_lock, when linked into kmmio_page_table.
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*/
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int count;
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bool scheduled_for_release;
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};
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struct kmmio_delayed_release {
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struct rcu_head rcu;
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struct kmmio_fault_page *release_list;
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};
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struct kmmio_context {
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struct kmmio_fault_page *fpage;
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struct kmmio_probe *probe;
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unsigned long saved_flags;
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unsigned long addr;
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int active;
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};
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static DEFINE_SPINLOCK(kmmio_lock);
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/* Protected by kmmio_lock */
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unsigned int kmmio_count;
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/* Read-protected by RCU, write-protected by kmmio_lock. */
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static struct list_head kmmio_page_table[KMMIO_PAGE_TABLE_SIZE];
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static LIST_HEAD(kmmio_probes);
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static struct list_head *kmmio_page_list(unsigned long addr)
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{
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unsigned int l;
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pte_t *pte = lookup_address(addr, &l);
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if (!pte)
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return NULL;
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addr &= page_level_mask(l);
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return &kmmio_page_table[hash_long(addr, KMMIO_PAGE_HASH_BITS)];
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}
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/* Accessed per-cpu */
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static DEFINE_PER_CPU(struct kmmio_context, kmmio_ctx);
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/*
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* this is basically a dynamic stabbing problem:
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* Could use the existing prio tree code or
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* Possible better implementations:
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* The Interval Skip List: A Data Structure for Finding All Intervals That
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* Overlap a Point (might be simple)
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* Space Efficient Dynamic Stabbing with Fast Queries - Mikkel Thorup
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*/
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/* Get the kmmio at this addr (if any). You must be holding RCU read lock. */
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static struct kmmio_probe *get_kmmio_probe(unsigned long addr)
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{
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struct kmmio_probe *p;
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list_for_each_entry_rcu(p, &kmmio_probes, list) {
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if (addr >= p->addr && addr < (p->addr + p->len))
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return p;
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}
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return NULL;
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}
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/* You must be holding RCU read lock. */
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static struct kmmio_fault_page *get_kmmio_fault_page(unsigned long addr)
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{
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struct list_head *head;
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struct kmmio_fault_page *f;
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unsigned int l;
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pte_t *pte = lookup_address(addr, &l);
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if (!pte)
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return NULL;
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addr &= page_level_mask(l);
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head = kmmio_page_list(addr);
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list_for_each_entry_rcu(f, head, list) {
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if (f->addr == addr)
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return f;
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}
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return NULL;
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}
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static void clear_pmd_presence(pmd_t *pmd, bool clear, pmdval_t *old)
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{
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pmd_t new_pmd;
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pmdval_t v = pmd_val(*pmd);
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if (clear) {
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*old = v;
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new_pmd = pmd_mknotpresent(*pmd);
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} else {
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/* Presume this has been called with clear==true previously */
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new_pmd = __pmd(*old);
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}
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set_pmd(pmd, new_pmd);
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}
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static void clear_pte_presence(pte_t *pte, bool clear, pteval_t *old)
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{
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pteval_t v = pte_val(*pte);
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if (clear) {
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*old = v;
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/* Nothing should care about address */
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pte_clear(&init_mm, 0, pte);
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} else {
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/* Presume this has been called with clear==true previously */
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set_pte_atomic(pte, __pte(*old));
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}
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}
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static int clear_page_presence(struct kmmio_fault_page *f, bool clear)
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{
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unsigned int level;
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pte_t *pte = lookup_address(f->addr, &level);
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if (!pte) {
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pr_err("no pte for addr 0x%08lx\n", f->addr);
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return -1;
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}
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switch (level) {
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case PG_LEVEL_2M:
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clear_pmd_presence((pmd_t *)pte, clear, &f->old_presence);
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break;
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case PG_LEVEL_4K:
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clear_pte_presence(pte, clear, &f->old_presence);
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break;
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default:
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pr_err("unexpected page level 0x%x.\n", level);
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return -1;
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}
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__flush_tlb_one_kernel(f->addr);
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return 0;
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}
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/*
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* Mark the given page as not present. Access to it will trigger a fault.
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*
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* Struct kmmio_fault_page is protected by RCU and kmmio_lock, but the
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* protection is ignored here. RCU read lock is assumed held, so the struct
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* will not disappear unexpectedly. Furthermore, the caller must guarantee,
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* that double arming the same virtual address (page) cannot occur.
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*
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* Double disarming on the other hand is allowed, and may occur when a fault
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* and mmiotrace shutdown happen simultaneously.
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*/
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static int arm_kmmio_fault_page(struct kmmio_fault_page *f)
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{
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int ret;
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WARN_ONCE(f->armed, KERN_ERR pr_fmt("kmmio page already armed.\n"));
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if (f->armed) {
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pr_warning("double-arm: addr 0x%08lx, ref %d, old %d\n",
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f->addr, f->count, !!f->old_presence);
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}
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ret = clear_page_presence(f, true);
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WARN_ONCE(ret < 0, KERN_ERR pr_fmt("arming at 0x%08lx failed.\n"),
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f->addr);
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f->armed = true;
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return ret;
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}
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/** Restore the given page to saved presence state. */
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static void disarm_kmmio_fault_page(struct kmmio_fault_page *f)
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{
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int ret = clear_page_presence(f, false);
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WARN_ONCE(ret < 0,
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KERN_ERR "kmmio disarming at 0x%08lx failed.\n", f->addr);
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f->armed = false;
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}
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/*
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* This is being called from do_page_fault().
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*
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* We may be in an interrupt or a critical section. Also prefecthing may
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* trigger a page fault. We may be in the middle of process switch.
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* We cannot take any locks, because we could be executing especially
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* within a kmmio critical section.
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*
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* Local interrupts are disabled, so preemption cannot happen.
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* Do not enable interrupts, do not sleep, and watch out for other CPUs.
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*/
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/*
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* Interrupts are disabled on entry as trap3 is an interrupt gate
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* and they remain disabled throughout this function.
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*/
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int kmmio_handler(struct pt_regs *regs, unsigned long addr)
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{
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struct kmmio_context *ctx;
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struct kmmio_fault_page *faultpage;
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int ret = 0; /* default to fault not handled */
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unsigned long page_base = addr;
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unsigned int l;
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pte_t *pte = lookup_address(addr, &l);
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if (!pte)
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return -EINVAL;
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page_base &= page_level_mask(l);
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/*
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* Preemption is now disabled to prevent process switch during
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* single stepping. We can only handle one active kmmio trace
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* per cpu, so ensure that we finish it before something else
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* gets to run. We also hold the RCU read lock over single
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* stepping to avoid looking up the probe and kmmio_fault_page
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* again.
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*/
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preempt_disable();
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rcu_read_lock();
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faultpage = get_kmmio_fault_page(page_base);
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if (!faultpage) {
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/*
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* Either this page fault is not caused by kmmio, or
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* another CPU just pulled the kmmio probe from under
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* our feet. The latter case should not be possible.
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*/
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goto no_kmmio;
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}
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ctx = &get_cpu_var(kmmio_ctx);
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if (ctx->active) {
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if (page_base == ctx->addr) {
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/*
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* A second fault on the same page means some other
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* condition needs handling by do_page_fault(), the
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* page really not being present is the most common.
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*/
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pr_debug("secondary hit for 0x%08lx CPU %d.\n",
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addr, smp_processor_id());
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if (!faultpage->old_presence)
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pr_info("unexpected secondary hit for address 0x%08lx on CPU %d.\n",
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addr, smp_processor_id());
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} else {
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/*
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* Prevent overwriting already in-flight context.
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* This should not happen, let's hope disarming at
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* least prevents a panic.
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*/
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pr_emerg("recursive probe hit on CPU %d, for address 0x%08lx. Ignoring.\n",
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smp_processor_id(), addr);
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pr_emerg("previous hit was at 0x%08lx.\n", ctx->addr);
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disarm_kmmio_fault_page(faultpage);
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}
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goto no_kmmio_ctx;
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}
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ctx->active++;
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ctx->fpage = faultpage;
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ctx->probe = get_kmmio_probe(page_base);
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ctx->saved_flags = (regs->flags & (X86_EFLAGS_TF | X86_EFLAGS_IF));
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ctx->addr = page_base;
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if (ctx->probe && ctx->probe->pre_handler)
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ctx->probe->pre_handler(ctx->probe, regs, addr);
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/*
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* Enable single-stepping and disable interrupts for the faulting
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* context. Local interrupts must not get enabled during stepping.
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*/
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regs->flags |= X86_EFLAGS_TF;
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regs->flags &= ~X86_EFLAGS_IF;
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/* Now we set present bit in PTE and single step. */
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disarm_kmmio_fault_page(ctx->fpage);
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/*
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* If another cpu accesses the same page while we are stepping,
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* the access will not be caught. It will simply succeed and the
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* only downside is we lose the event. If this becomes a problem,
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* the user should drop to single cpu before tracing.
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*/
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put_cpu_var(kmmio_ctx);
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return 1; /* fault handled */
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no_kmmio_ctx:
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put_cpu_var(kmmio_ctx);
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no_kmmio:
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rcu_read_unlock();
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preempt_enable_no_resched();
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return ret;
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}
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/*
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* Interrupts are disabled on entry as trap1 is an interrupt gate
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* and they remain disabled throughout this function.
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* This must always get called as the pair to kmmio_handler().
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*/
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static int post_kmmio_handler(unsigned long condition, struct pt_regs *regs)
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{
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int ret = 0;
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struct kmmio_context *ctx = &get_cpu_var(kmmio_ctx);
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if (!ctx->active) {
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/*
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* debug traps without an active context are due to either
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* something external causing them (f.e. using a debugger while
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* mmio tracing enabled), or erroneous behaviour
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*/
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pr_warning("unexpected debug trap on CPU %d.\n",
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smp_processor_id());
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goto out;
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}
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if (ctx->probe && ctx->probe->post_handler)
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ctx->probe->post_handler(ctx->probe, condition, regs);
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/* Prevent racing against release_kmmio_fault_page(). */
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spin_lock(&kmmio_lock);
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if (ctx->fpage->count)
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arm_kmmio_fault_page(ctx->fpage);
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spin_unlock(&kmmio_lock);
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regs->flags &= ~X86_EFLAGS_TF;
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regs->flags |= ctx->saved_flags;
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/* These were acquired in kmmio_handler(). */
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ctx->active--;
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BUG_ON(ctx->active);
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rcu_read_unlock();
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preempt_enable_no_resched();
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/*
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* if somebody else is singlestepping across a probe point, flags
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* will have TF set, in which case, continue the remaining processing
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* of do_debug, as if this is not a probe hit.
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*/
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if (!(regs->flags & X86_EFLAGS_TF))
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ret = 1;
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out:
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put_cpu_var(kmmio_ctx);
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return ret;
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}
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/* You must be holding kmmio_lock. */
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static int add_kmmio_fault_page(unsigned long addr)
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{
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struct kmmio_fault_page *f;
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f = get_kmmio_fault_page(addr);
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if (f) {
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if (!f->count)
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arm_kmmio_fault_page(f);
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f->count++;
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return 0;
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}
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f = kzalloc(sizeof(*f), GFP_ATOMIC);
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if (!f)
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return -1;
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f->count = 1;
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f->addr = addr;
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if (arm_kmmio_fault_page(f)) {
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kfree(f);
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return -1;
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}
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list_add_rcu(&f->list, kmmio_page_list(f->addr));
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return 0;
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}
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/* You must be holding kmmio_lock. */
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static void release_kmmio_fault_page(unsigned long addr,
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struct kmmio_fault_page **release_list)
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{
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struct kmmio_fault_page *f;
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f = get_kmmio_fault_page(addr);
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if (!f)
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return;
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f->count--;
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BUG_ON(f->count < 0);
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if (!f->count) {
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disarm_kmmio_fault_page(f);
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if (!f->scheduled_for_release) {
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f->release_next = *release_list;
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*release_list = f;
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f->scheduled_for_release = true;
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}
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}
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}
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/*
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* With page-unaligned ioremaps, one or two armed pages may contain
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* addresses from outside the intended mapping. Events for these addresses
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* are currently silently dropped. The events may result only from programming
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* mistakes by accessing addresses before the beginning or past the end of a
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* mapping.
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*/
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int register_kmmio_probe(struct kmmio_probe *p)
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{
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unsigned long flags;
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int ret = 0;
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unsigned long size = 0;
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unsigned long addr = p->addr & PAGE_MASK;
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const unsigned long size_lim = p->len + (p->addr & ~PAGE_MASK);
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unsigned int l;
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pte_t *pte;
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spin_lock_irqsave(&kmmio_lock, flags);
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if (get_kmmio_probe(addr)) {
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ret = -EEXIST;
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goto out;
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}
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pte = lookup_address(addr, &l);
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if (!pte) {
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ret = -EINVAL;
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goto out;
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}
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kmmio_count++;
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list_add_rcu(&p->list, &kmmio_probes);
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while (size < size_lim) {
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if (add_kmmio_fault_page(addr + size))
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pr_err("Unable to set page fault.\n");
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size += page_level_size(l);
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}
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out:
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spin_unlock_irqrestore(&kmmio_lock, flags);
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/*
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* XXX: What should I do here?
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* Here was a call to global_flush_tlb(), but it does not exist
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* anymore. It seems it's not needed after all.
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*/
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return ret;
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}
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EXPORT_SYMBOL(register_kmmio_probe);
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static void rcu_free_kmmio_fault_pages(struct rcu_head *head)
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{
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struct kmmio_delayed_release *dr = container_of(
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head,
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struct kmmio_delayed_release,
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rcu);
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struct kmmio_fault_page *f = dr->release_list;
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while (f) {
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struct kmmio_fault_page *next = f->release_next;
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BUG_ON(f->count);
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kfree(f);
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f = next;
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}
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kfree(dr);
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}
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static void remove_kmmio_fault_pages(struct rcu_head *head)
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{
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struct kmmio_delayed_release *dr =
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container_of(head, struct kmmio_delayed_release, rcu);
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struct kmmio_fault_page *f = dr->release_list;
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struct kmmio_fault_page **prevp = &dr->release_list;
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unsigned long flags;
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spin_lock_irqsave(&kmmio_lock, flags);
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while (f) {
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if (!f->count) {
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list_del_rcu(&f->list);
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prevp = &f->release_next;
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} else {
|
|
*prevp = f->release_next;
|
|
f->release_next = NULL;
|
|
f->scheduled_for_release = false;
|
|
}
|
|
f = *prevp;
|
|
}
|
|
spin_unlock_irqrestore(&kmmio_lock, flags);
|
|
|
|
/* This is the real RCU destroy call. */
|
|
call_rcu(&dr->rcu, rcu_free_kmmio_fault_pages);
|
|
}
|
|
|
|
/*
|
|
* Remove a kmmio probe. You have to synchronize_rcu() before you can be
|
|
* sure that the callbacks will not be called anymore. Only after that
|
|
* you may actually release your struct kmmio_probe.
|
|
*
|
|
* Unregistering a kmmio fault page has three steps:
|
|
* 1. release_kmmio_fault_page()
|
|
* Disarm the page, wait a grace period to let all faults finish.
|
|
* 2. remove_kmmio_fault_pages()
|
|
* Remove the pages from kmmio_page_table.
|
|
* 3. rcu_free_kmmio_fault_pages()
|
|
* Actually free the kmmio_fault_page structs as with RCU.
|
|
*/
|
|
void unregister_kmmio_probe(struct kmmio_probe *p)
|
|
{
|
|
unsigned long flags;
|
|
unsigned long size = 0;
|
|
unsigned long addr = p->addr & PAGE_MASK;
|
|
const unsigned long size_lim = p->len + (p->addr & ~PAGE_MASK);
|
|
struct kmmio_fault_page *release_list = NULL;
|
|
struct kmmio_delayed_release *drelease;
|
|
unsigned int l;
|
|
pte_t *pte;
|
|
|
|
pte = lookup_address(addr, &l);
|
|
if (!pte)
|
|
return;
|
|
|
|
spin_lock_irqsave(&kmmio_lock, flags);
|
|
while (size < size_lim) {
|
|
release_kmmio_fault_page(addr + size, &release_list);
|
|
size += page_level_size(l);
|
|
}
|
|
list_del_rcu(&p->list);
|
|
kmmio_count--;
|
|
spin_unlock_irqrestore(&kmmio_lock, flags);
|
|
|
|
if (!release_list)
|
|
return;
|
|
|
|
drelease = kmalloc(sizeof(*drelease), GFP_ATOMIC);
|
|
if (!drelease) {
|
|
pr_crit("leaking kmmio_fault_page objects.\n");
|
|
return;
|
|
}
|
|
drelease->release_list = release_list;
|
|
|
|
/*
|
|
* This is not really RCU here. We have just disarmed a set of
|
|
* pages so that they cannot trigger page faults anymore. However,
|
|
* we cannot remove the pages from kmmio_page_table,
|
|
* because a probe hit might be in flight on another CPU. The
|
|
* pages are collected into a list, and they will be removed from
|
|
* kmmio_page_table when it is certain that no probe hit related to
|
|
* these pages can be in flight. RCU grace period sounds like a
|
|
* good choice.
|
|
*
|
|
* If we removed the pages too early, kmmio page fault handler might
|
|
* not find the respective kmmio_fault_page and determine it's not
|
|
* a kmmio fault, when it actually is. This would lead to madness.
|
|
*/
|
|
call_rcu(&drelease->rcu, remove_kmmio_fault_pages);
|
|
}
|
|
EXPORT_SYMBOL(unregister_kmmio_probe);
|
|
|
|
static int
|
|
kmmio_die_notifier(struct notifier_block *nb, unsigned long val, void *args)
|
|
{
|
|
struct die_args *arg = args;
|
|
unsigned long* dr6_p = (unsigned long *)ERR_PTR(arg->err);
|
|
|
|
if (val == DIE_DEBUG && (*dr6_p & DR_STEP))
|
|
if (post_kmmio_handler(*dr6_p, arg->regs) == 1) {
|
|
/*
|
|
* Reset the BS bit in dr6 (pointed by args->err) to
|
|
* denote completion of processing
|
|
*/
|
|
*dr6_p &= ~DR_STEP;
|
|
return NOTIFY_STOP;
|
|
}
|
|
|
|
return NOTIFY_DONE;
|
|
}
|
|
|
|
static struct notifier_block nb_die = {
|
|
.notifier_call = kmmio_die_notifier
|
|
};
|
|
|
|
int kmmio_init(void)
|
|
{
|
|
int i;
|
|
|
|
for (i = 0; i < KMMIO_PAGE_TABLE_SIZE; i++)
|
|
INIT_LIST_HEAD(&kmmio_page_table[i]);
|
|
|
|
return register_die_notifier(&nb_die);
|
|
}
|
|
|
|
void kmmio_cleanup(void)
|
|
{
|
|
int i;
|
|
|
|
unregister_die_notifier(&nb_die);
|
|
for (i = 0; i < KMMIO_PAGE_TABLE_SIZE; i++) {
|
|
WARN_ONCE(!list_empty(&kmmio_page_table[i]),
|
|
KERN_ERR "kmmio_page_table not empty at cleanup, any further tracing will leak memory.\n");
|
|
}
|
|
}
|