From 15969cbd494dc7a376a2faea78c9de2ac27a1b89 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Tue, 14 Jun 2022 23:15:40 +0200 Subject: [PATCH] x86/ftrace: Use alternative RET encoding Use the return thunk in ftrace trampolines, if needed. Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Borislav Petkov Reviewed-by: Josh Poimboeuf Signed-off-by: Borislav Petkov (backported from commit 1f001e9da6bbf482311e45e48f53c2bd2179e59c) [cascardo: use memcpy(text_gen_insn) as there is no __text_gen_insn] CVE-2022-29900 CVE-2022-29901 Signed-off-by: Thadeu Lima de Souza Cascardo --- arch/x86/kernel/ftrace.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c index b491be547a0a..6bb479ce1ae4 100644 --- a/arch/x86/kernel/ftrace.c +++ b/arch/x86/kernel/ftrace.c @@ -308,7 +308,7 @@ union ftrace_op_code_union { } __attribute__((packed)); }; -#define RET_SIZE 1 + IS_ENABLED(CONFIG_SLS) +#define RET_SIZE (IS_ENABLED(CONFIG_RETPOLINE) ? 5 : 1 + IS_ENABLED(CONFIG_SLS)) static unsigned long create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size) @@ -364,7 +364,10 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size) goto fail; ip = trampoline + size; - memcpy(ip, retq, RET_SIZE); + if (cpu_feature_enabled(X86_FEATURE_RETHUNK)) + memcpy(ip, text_gen_insn(JMP32_INSN_OPCODE, ip, &__x86_return_thunk), JMP32_INSN_SIZE); + else + memcpy(ip, retq, sizeof(retq)); /* No need to test direct calls on created trampolines */ if (ops->flags & FTRACE_OPS_FL_SAVE_REGS) { -- 2.39.2