From 082c4c815252ea333b0f3a51e336df60c2314fe2 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Thu, 27 Oct 2022 11:28:15 +0200 Subject: x86/cfi: Boot time selection of CFI scheme Add the "cfi=" boot parameter to allow people to select a CFI scheme at boot time. Mostly useful for development / debugging. Requested-by: Kees Cook Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Kees Cook Link: https://lore.kernel.org/r/20221027092842.699804264@infradead.org --- arch/x86/kernel/alternative.c | 99 +++++++++++++++++++++++++++++++++++-------- 1 file changed, 81 insertions(+), 18 deletions(-) (limited to 'arch/x86/kernel/alternative.c') diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index 91b0e63a6238..9d3b58748ca5 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -702,6 +702,47 @@ void __init_or_module noinline apply_ibt_endbr(s32 *start, s32 *end) { } #endif /* CONFIG_X86_KERNEL_IBT */ #ifdef CONFIG_FINEIBT + +enum cfi_mode { + CFI_DEFAULT, + CFI_OFF, + CFI_KCFI, + CFI_FINEIBT, +}; + +static enum cfi_mode cfi_mode __ro_after_init = CFI_DEFAULT; + +static __init int cfi_parse_cmdline(char *str) +{ + if (!str) + return -EINVAL; + + while (str) { + char *next = strchr(str, ','); + if (next) { + *next = 0; + next++; + } + + if (!strcmp(str, "auto")) { + cfi_mode = CFI_DEFAULT; + } else if (!strcmp(str, "off")) { + cfi_mode = CFI_OFF; + } else if (!strcmp(str, "kcfi")) { + cfi_mode = CFI_KCFI; + } else if (!strcmp(str, "fineibt")) { + cfi_mode = CFI_FINEIBT; + } else { + pr_err("Ignoring unknown cfi option (%s).", str); + } + + str = next; + } + + return 0; +} +early_param("cfi", cfi_parse_cmdline); + /* * kCFI FineIBT * @@ -868,30 +909,52 @@ static void __apply_fineibt(s32 *start_retpoline, s32 *end_retpoline, "FineIBT preamble wrong size: %ld", fineibt_preamble_size)) return; - if (!HAS_KERNEL_IBT || !cpu_feature_enabled(X86_FEATURE_IBT)) + if (cfi_mode == CFI_DEFAULT) { + cfi_mode = CFI_KCFI; + if (HAS_KERNEL_IBT && cpu_feature_enabled(X86_FEATURE_IBT)) + cfi_mode = CFI_FINEIBT; + } + + switch (cfi_mode) { + case CFI_OFF: + ret = cfi_disable_callers(start_retpoline, end_retpoline); + if (ret) + goto err; + + if (builtin) + pr_info("Disabling CFI\n"); return; - /* - * Rewrite the callers to not use the __cfi_ stubs, such that we might - * rewrite them. This disables all CFI. If this succeeds but any of the - * later stages fails, we're without CFI. - */ - ret = cfi_disable_callers(start_retpoline, end_retpoline); - if (ret) - goto err; + case CFI_KCFI: + if (builtin) + pr_info("Using kCFI\n"); + return; - ret = cfi_rewrite_preamble(start_cfi, end_cfi); - if (ret) - goto err; + case CFI_FINEIBT: + /* + * Rewrite the callers to not use the __cfi_ stubs, such that we might + * rewrite them. This disables all CFI. If this succeeds but any of the + * later stages fails, we're without CFI. + */ + ret = cfi_disable_callers(start_retpoline, end_retpoline); + if (ret) + goto err; + + ret = cfi_rewrite_preamble(start_cfi, end_cfi); + if (ret) + goto err; - ret = cfi_rewrite_callers(start_retpoline, end_retpoline); - if (ret) - goto err; + ret = cfi_rewrite_callers(start_retpoline, end_retpoline); + if (ret) + goto err; - if (builtin) - pr_info("Using FineIBT CFI\n"); + if (builtin) + pr_info("Using FineIBT CFI\n"); + return; - return; + default: + break; + } err: pr_err("Something went horribly wrong trying to rewrite the CFI implementation.\n"); -- cgit v1.2.3