arm64: module/ftrace: intialize PLT at load time
Currently we lazily-initialize a module's ftrace PLT at runtime when we install the first ftrace call. To do so we have to apply a number of sanity checks, transiently mark the module text as RW, and perform an IPI as part of handling Neoverse-N1 erratum #1542419. We only expect the ftrace trampoline to point at ftrace_caller() (AKA FTRACE_ADDR), so let's simplify all of this by intializing the PLT at module load time, before the module loader marks the module RO and performs the intial I-cache maintenance for the module. Thus we can rely on the module having been correctly intialized, and can simplify the runtime work necessary to install an ftrace call in a module. This will also allow for the removal of module_disable_ro(). Tested by forcing ftrace_make_call() to use the module PLT, and then loading up a module after setting up ftrace with: | echo ":mod:<module-name>" > set_ftrace_filter; | echo function > current_tracer; | modprobe <module-name> Since FTRACE_ADDR is only defined when CONFIG_DYNAMIC_FTRACE is selected, we wrap its use along with most of module_init_ftrace_plt() with ifdeffery rather than using IS_ENABLED(). Signed-off-by: Mark Rutland <mark.rutland@arm.com> Reviewed-by: Amit Daniel Kachhap <amit.kachhap@arm.com> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Reviewed-by: Torsten Duwe <duwe@suse.de> Tested-by: Amit Daniel Kachhap <amit.kachhap@arm.com> Tested-by: Torsten Duwe <duwe@suse.de> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: James Morse <james.morse@arm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Will Deacon <will@kernel.org>
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@ -73,9 +73,21 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
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if (offset < -SZ_128M || offset >= SZ_128M) {
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if (offset < -SZ_128M || offset >= SZ_128M) {
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#ifdef CONFIG_ARM64_MODULE_PLTS
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#ifdef CONFIG_ARM64_MODULE_PLTS
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struct plt_entry trampoline, *dst;
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struct module *mod;
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struct module *mod;
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/*
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* There is only one ftrace trampoline per module. For now,
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* this is not a problem since on arm64, all dynamic ftrace
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* invocations are routed via ftrace_caller(). This will need
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* to be revisited if support for multiple ftrace entry points
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* is added in the future, but for now, the pr_err() below
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* deals with a theoretical issue only.
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*/
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if (addr != FTRACE_ADDR) {
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pr_err("ftrace: far branches to multiple entry points unsupported inside a single module\n");
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return -EINVAL;
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}
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/*
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/*
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* On kernels that support module PLTs, the offset between the
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* On kernels that support module PLTs, the offset between the
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* branch instruction and its target may legally exceed the
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* branch instruction and its target may legally exceed the
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@ -93,46 +105,7 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
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if (WARN_ON(!mod))
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if (WARN_ON(!mod))
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return -EINVAL;
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return -EINVAL;
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/*
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addr = (unsigned long)mod->arch.ftrace_trampoline;
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* There is only one ftrace trampoline per module. For now,
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* this is not a problem since on arm64, all dynamic ftrace
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* invocations are routed via ftrace_caller(). This will need
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* to be revisited if support for multiple ftrace entry points
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* is added in the future, but for now, the pr_err() below
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* deals with a theoretical issue only.
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*
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* Note that PLTs are place relative, and plt_entries_equal()
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* checks whether they point to the same target. Here, we need
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* to check if the actual opcodes are in fact identical,
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* regardless of the offset in memory so use memcmp() instead.
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*/
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dst = mod->arch.ftrace_trampoline;
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trampoline = get_plt_entry(addr, dst);
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if (memcmp(dst, &trampoline, sizeof(trampoline))) {
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if (plt_entry_is_initialized(dst)) {
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pr_err("ftrace: far branches to multiple entry points unsupported inside a single module\n");
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return -EINVAL;
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}
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/* point the trampoline to our ftrace entry point */
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module_disable_ro(mod);
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*dst = trampoline;
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module_enable_ro(mod, true);
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/*
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* Ensure updated trampoline is visible to instruction
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* fetch before we patch in the branch. Although the
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* architecture doesn't require an IPI in this case,
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* Neoverse-N1 erratum #1542419 does require one
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* if the TLB maintenance in module_enable_ro() is
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* skipped due to rodata_enabled. It doesn't seem worth
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* it to make it conditional given that this is
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* certainly not a fast-path.
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*/
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flush_icache_range((unsigned long)&dst[0],
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(unsigned long)&dst[1]);
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}
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addr = (unsigned long)dst;
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#else /* CONFIG_ARM64_MODULE_PLTS */
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#else /* CONFIG_ARM64_MODULE_PLTS */
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return -EINVAL;
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return -EINVAL;
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#endif /* CONFIG_ARM64_MODULE_PLTS */
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#endif /* CONFIG_ARM64_MODULE_PLTS */
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@ -9,6 +9,7 @@
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#include <linux/bitops.h>
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#include <linux/bitops.h>
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#include <linux/elf.h>
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#include <linux/elf.h>
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#include <linux/ftrace.h>
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#include <linux/gfp.h>
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#include <linux/gfp.h>
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#include <linux/kasan.h>
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#include <linux/kasan.h>
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#include <linux/kernel.h>
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#include <linux/kernel.h>
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@ -485,24 +486,33 @@ static const Elf_Shdr *find_section(const Elf_Ehdr *hdr,
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return NULL;
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return NULL;
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}
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}
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static int module_init_ftrace_plt(const Elf_Ehdr *hdr,
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const Elf_Shdr *sechdrs,
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struct module *mod)
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{
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#if defined(CONFIG_ARM64_MODULE_PLTS) && defined(CONFIG_DYNAMIC_FTRACE)
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const Elf_Shdr *s;
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struct plt_entry *plt;
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s = find_section(hdr, sechdrs, ".text.ftrace_trampoline");
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if (!s)
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return -ENOEXEC;
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plt = (void *)s->sh_addr;
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*plt = get_plt_entry(FTRACE_ADDR, plt);
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mod->arch.ftrace_trampoline = plt;
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#endif
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return 0;
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}
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int module_finalize(const Elf_Ehdr *hdr,
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int module_finalize(const Elf_Ehdr *hdr,
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const Elf_Shdr *sechdrs,
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const Elf_Shdr *sechdrs,
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struct module *me)
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struct module *me)
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{
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{
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const Elf_Shdr *s;
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const Elf_Shdr *s;
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s = find_section(hdr, sechdrs, ".altinstructions");
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s = find_section(hdr, sechdrs, ".altinstructions");
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if (s)
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if (s)
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apply_alternatives_module((void *)s->sh_addr, s->sh_size);
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apply_alternatives_module((void *)s->sh_addr, s->sh_size);
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#ifdef CONFIG_ARM64_MODULE_PLTS
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return module_init_ftrace_plt(hdr, sechdrs, me);
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if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE)) {
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s = find_section(hdr, sechdrs, ".text.ftrace_trampoline");
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if (!s)
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return -ENOEXEC;
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me->arch.ftrace_trampoline = (void *)s->sh_addr;
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}
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#endif
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return 0;
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}
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}
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