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Commit 30b9da0e authored by Will Deacon's avatar Will Deacon Committed by Greg Kroah-Hartman
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arm64: ftrace: Ensure module ftrace trampoline is coherent with I-side 



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 (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 <ard.biesheuvel@linaro.org>
Cc: James Morse <james.morse@arm.com>
Cc: <stable@vger.kernel.org>
Fixes: be0f272b ("arm64: ftrace: emit ftrace-mod.o contents through code")
Signed-off-by: default avatarWill Deacon <will@kernel.org>
Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent a1cd2f70

arch/arm64/kernel/ftrace.c

+12 −9
Original line number Diff line number Diff line
@@ -76,7 +76,7 @@ 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;



		/*
@@ -104,24 +104,27 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr) 
		 * 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 */