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Commit 4e69ecf4 authored by Ard Biesheuvel's avatar Ard Biesheuvel Committed by Catalin Marinas
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arm64/module: ftrace: deal with place relative nature of PLTs 



Another bodge for the ftrace PLT code: plt_entries_equal() now takes
the place relative nature of the ADRP/ADD based PLT entries into
account, which means that a struct trampoline instance on the stack
is no longer equal to the same set of opcodes in the module struct,
given that they don't point to the same place in memory anymore.

Work around this by using memcmp() in the ftrace PLT handling code.

Acked-by: default avatarWill Deacon <will.deacon@arm.com>
Tested-by: default avatardann frazier <dann.frazier@canonical.com>
Signed-off-by: default avatarArd Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent d4d18e3e

arch/arm64/kernel/ftrace.c

+7 −2
Original line number Diff line number Diff line
@@ -103,10 +103,15 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr) 
		 * to be revisited if support for multiple ftrace entry points

		 * is added in the future, but for now, the pr_err() below

		 * deals with a theoretical issue only.

		 *

		 * Note that PLTs are place relative, and plt_entries_equal()

		 * checks whether they point to the same target. Here, we need

		 * 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 (!plt_entries_equal(mod->arch.ftrace_trampoline,

				       &trampoline)) {

		if (memcmp(mod->arch.ftrace_trampoline, &trampoline,

			   sizeof(trampoline))) {

			if (plt_entry_is_initialized(mod->arch.ftrace_trampoline)) {

				pr_err("ftrace: far branches to multiple entry points unsupported inside a single module\n");

				return -EINVAL;