Commit b6143d10 authored by Will Deacon's avatar Will Deacon Committed by Catalin Marinas
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arm64: ftrace: Ensure module ftrace trampoline is coherent with I-side

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 (e71a4e1b ("arm64: ftrace: add support for far
branches to dynamic ftrace")). Since no instructions were being patched,
no cache maintenance was needed. However, later in be0f272b ("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 <>
Cc: James Morse <>
Cc: <>
Fixes: be0f272b

 ("arm64: ftrace: emit ftrace-mod.o contents through code")
Signed-off-by: default avatarWill Deacon <>
Signed-off-by: default avatarCatalin Marinas <>
parent 5717fe5a
......@@ -73,7 +73,7 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
if (offset < -SZ_128M || offset >= SZ_128M) {
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 */
*mod->arch.ftrace_trampoline = trampoline;
*dst = trampoline;
module_enable_ro(mod, true);
/* update trampoline before patching in the branch */
* 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;
return -EINVAL;
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