From: Will Deacon will@kernel.org
commit b6143d10d23ebb4a77af311e8b8b7f019d0163e6 upstream.
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@linaro.org Cc: James Morse james.morse@arm.com Cc: stable@vger.kernel.org Fixes: be0f272bfc83 ("arm64: ftrace: emit ftrace-mod.o contents through code") Signed-off-by: Will Deacon will@kernel.org Signed-off-by: Catalin Marinas catalin.marinas@arm.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/arm64/kernel/ftrace.c | 21 ++++++++++++--------- 1 file changed, 12 insertions(+), 9 deletions(-)
--- a/arch/arm64/kernel/ftrace.c +++ b/arch/arm64/kernel/ftrace.c @@ -76,7 +76,7 @@ int ftrace_make_call(struct dyn_ftrace *
if (offset < -SZ_128M || offset >= SZ_128M) { #ifdef CONFIG_ARM64_MODULE_PLTS - struct plt_entry trampoline; + struct plt_entry trampoline, *dst; struct module *mod;
/* @@ -104,24 +104,27 @@ int ftrace_make_call(struct dyn_ftrace * * is added in the future, but for now, the pr_err() below * deals with a theoretical issue only. */ + dst = mod->arch.ftrace_trampoline; trampoline = get_plt_entry(addr); - if (!plt_entries_equal(mod->arch.ftrace_trampoline, - &trampoline)) { - if (!plt_entries_equal(mod->arch.ftrace_trampoline, - &(struct plt_entry){})) { + if (!plt_entries_equal(dst, &trampoline)) { + if (!plt_entries_equal(dst, &(struct plt_entry){})) { 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 */