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seccomp: Allow arch code to provide seccomp_data 

populate_seccomp_data is expensive: it works by inspecting
task_pt_regs and various other bits to piece together all the
information, and it's does so in multiple partially redundant steps.

Arch-specific code in the syscall entry path can do much better.

Admittedly this adds a bit of additional room for error, but the
speedup should be worth it.

Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Kees Cook <keescook@chromium.org>
hifive-unleashed-5.1
Andy Lutomirski 2014-07-21 18:49:16 -07:00 committed by Kees Cook
parent 13aa72f0fd
commit d39bd00dea
2 changed files with 20 additions and 14 deletions
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2
include/linux/seccomp.h
View File

@ -39,7 +39,7 @@ static inline int secure_computing(void)
#define SECCOMP_PHASE1_OK 0
#define SECCOMP_PHASE1_SKIP 1
extern u32 seccomp_phase1(void);
extern u32 seccomp_phase1(struct seccomp_data *sd);
int seccomp_phase2(u32 phase1_result);
#else
extern void secure_computing_strict(int this_syscall);

32
kernel/seccomp.c
View File

@ -173,10 +173,10 @@ static int seccomp_check_filter(struct sock_filter *filter, unsigned int flen)
*
* Returns valid seccomp BPF response codes.
*/
static u32 seccomp_run_filters(void)
static u32 seccomp_run_filters(struct seccomp_data *sd)
{
struct seccomp_filter *f = ACCESS_ONCE(current->seccomp.filter);
struct seccomp_data sd;
struct seccomp_data sd_local;
u32 ret = SECCOMP_RET_ALLOW;
/* Ensure unexpected behavior doesn't result in failing open. */
@ -186,14 +186,17 @@ static u32 seccomp_run_filters(void)
/* Make sure cross-thread synced filter points somewhere sane. */
smp_read_barrier_depends();
populate_seccomp_data(&sd);
if (!sd) {
populate_seccomp_data(&sd_local);
sd = &sd_local;
}
/*
* All filters in the list are evaluated and the lowest BPF return
* value always takes priority (ignoring the DATA).
*/
for (; f; f = f->prev) {
u32 cur_ret = BPF_PROG_RUN(f->prog, (void *)&sd);
u32 cur_ret = BPF_PROG_RUN(f->prog, (void *)sd);
if ((cur_ret & SECCOMP_RET_ACTION) < (ret & SECCOMP_RET_ACTION))
ret = cur_ret;
@ -599,7 +602,7 @@ void secure_computing_strict(int this_syscall)
#else
int __secure_computing(void)
{
u32 phase1_result = seccomp_phase1();
u32 phase1_result = seccomp_phase1(NULL);
if (likely(phase1_result == SECCOMP_PHASE1_OK))
return 0;
@ -610,7 +613,7 @@ int __secure_computing(void)
}
#ifdef CONFIG_SECCOMP_FILTER
static u32 __seccomp_phase1_filter(int this_syscall, struct pt_regs *regs)
static u32 __seccomp_phase1_filter(int this_syscall, struct seccomp_data *sd)
{
u32 filter_ret, action;
int data;
@ -621,20 +624,20 @@ static u32 __seccomp_phase1_filter(int this_syscall, struct pt_regs *regs)
*/
rmb();
filter_ret = seccomp_run_filters();
filter_ret = seccomp_run_filters(sd);
data = filter_ret & SECCOMP_RET_DATA;
action = filter_ret & SECCOMP_RET_ACTION;
switch (action) {
case SECCOMP_RET_ERRNO:
/* Set the low-order 16-bits as a errno. */
syscall_set_return_value(current, regs,
syscall_set_return_value(current, task_pt_regs(current),
-data, 0);
goto skip;
case SECCOMP_RET_TRAP:
/* Show the handler the original registers. */
syscall_rollback(current, regs);
syscall_rollback(current, task_pt_regs(current));
/* Let the filter pass back 16 bits of data. */
seccomp_send_sigsys(this_syscall, data);
goto skip;
@ -661,11 +664,14 @@ skip:
/**
* seccomp_phase1() - run fast path seccomp checks on the current syscall
* @arg sd: The seccomp_data or NULL
*
* This only reads pt_regs via the syscall_xyz helpers. The only change
* it will make to pt_regs is via syscall_set_return_value, and it will
* only do that if it returns SECCOMP_PHASE1_SKIP.
*
* If sd is provided, it will not read pt_regs at all.
*
* It may also call do_exit or force a signal; these actions must be
* safe.
*
@ -679,11 +685,11 @@ skip:
* If it returns anything else, then the return value should be passed
* to seccomp_phase2 from a context in which ptrace hooks are safe.
*/
u32 seccomp_phase1(void)
u32 seccomp_phase1(struct seccomp_data *sd)
{
int mode = current->seccomp.mode;
struct pt_regs *regs = task_pt_regs(current);
int this_syscall = syscall_get_nr(current, regs);
int this_syscall = sd ? sd->nr :
syscall_get_nr(current, task_pt_regs(current));
switch (mode) {
case SECCOMP_MODE_STRICT:
@ -691,7 +697,7 @@ u32 seccomp_phase1(void)
return SECCOMP_PHASE1_OK;
#ifdef CONFIG_SECCOMP_FILTER
case SECCOMP_MODE_FILTER:
return __seccomp_phase1_filter(this_syscall, regs);
return __seccomp_phase1_filter(this_syscall, sd);
#endif
default:
BUG();