The initial support for dynamic ftrace trampolines in modules made use
of an indirect branch which loaded its target from the beginning of
a special section (e71a4e1bebaf7 ("arm64: ftrace: add support for far
branches to dynamic ftrace")). Since no instructions were being patched,
no cache maintenance was needed. However, later in be0f272bfc83 ("arm64:
ftrace: emit ftrace-mod.o contents through code") this code was reworked
to output the trampoline instructions directly into the PLT entry but,
unfortunately, the necessary cache maintenance was overlooked.
Add a call to __flush_icache_range() after writing the new trampoline
instructions but before patching in the branch to the trampoline.
Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: James Morse <james.morse@xxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Fixes: be0f272bfc83 ("arm64: ftrace: emit ftrace-mod.o contents through code")
Signed-off-by: Will Deacon <will@xxxxxxxxxx>
---
arch/arm64/kernel/ftrace.c | 22 +++++++++++++---------
1 file changed, 13 insertions(+), 9 deletions(-)
diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c
index 1285c7b2947f..171773257974 100644
--- a/arch/arm64/kernel/ftrace.c
+++ b/arch/arm64/kernel/ftrace.c
@@ -73,7 +73,7 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
if (offset < -SZ_128M || offset >= SZ_128M) {
#ifdef CONFIG_ARM64_MODULE_PLTS
- struct plt_entry trampoline;
+ struct plt_entry trampoline, *dst;
struct module *mod;
/*
@@ -106,23 +106,27 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
* to check if the actual opcodes are in fact identical,
* regardless of the offset in memory so use memcmp() instead.
*/
- trampoline = get_plt_entry(addr, mod->arch.ftrace_trampoline);
- if (memcmp(mod->arch.ftrace_trampoline, &trampoline,
- sizeof(trampoline))) {
- if (plt_entry_is_initialized(mod->arch.ftrace_trampoline)) {
+ dst = mod->arch.ftrace_trampoline;
+ trampoline = get_plt_entry(addr, dst);
+ if (memcmp(dst, &trampoline, sizeof(trampoline))) {
+ if (plt_entry_is_initialized(dst)) {
pr_err("ftrace: far branches to multiple entry points unsupported inside a single module\n");
return -EINVAL;
}
/* point the trampoline to our ftrace entry point */
module_disable_ro(mod);
- *mod->arch.ftrace_trampoline = trampoline;
+ *dst = trampoline;
module_enable_ro(mod, true);
- /* update trampoline before patching in the branch */
- smp_wmb();
+ /*
+ * Ensure updated trampoline is visible to instruction
+ * fetch before we patch in the branch.
+ */
+ __flush_icache_range((unsigned long)&dst[0],
+ (unsigned long)&dst[1]);
}
- addr = (unsigned long)(void *)mod->arch.ftrace_trampoline;
+ addr = (unsigned long)dst;
#else /* CONFIG_ARM64_MODULE_PLTS */
return -EINVAL;
#endif /* CONFIG_ARM64_MODULE_PLTS */
--
2.11.0
