From 8c6a490e404fe82b53bbafe0f0eeef10605617f7 Mon Sep 17 00:00:00 2001 From: Mark Rutland Date: Fri, 6 May 2022 13:11:45 +0100 Subject: [PATCH] lkdtm/stackleak: fix CONFIG_GCC_PLUGIN_STACKLEAK=n Recent rework broke building LKDTM when CONFIG_GCC_PLUGIN_STACKLEAK=n. This patch fixes that breakage. Prior to recent stackleak rework, the LKDTM STACKLEAK_ERASING code could be built when the kernel was not built with stackleak support, and would run a test that would almost certainly fail (or pass by sheer cosmic coincidence), e.g. | # echo STACKLEAK_ERASING > /sys/kernel/debug/provoke-crash/DIRECT | lkdtm: Performing direct entry STACKLEAK_ERASING | lkdtm: checking unused part of the thread stack (15560 bytes)... | lkdtm: FAIL: the erased part is not found (checked 15560 bytes) | lkdtm: FAIL: the thread stack is NOT properly erased! | lkdtm: This is probably expected, since this kernel (5.18.0-rc2 aarch64) was built *without* CONFIG_GCC_PLUGIN_STACKLEAK=y The recent rework to the test made it more accurate by using helpers which are only defined when CONFIG_GCC_PLUGIN_STACKLEAK=y, and so when building LKDTM when CONFIG_GCC_PLUGIN_STACKLEAK=n, we get a build failure: | drivers/misc/lkdtm/stackleak.c: In function 'check_stackleak_irqoff': | drivers/misc/lkdtm/stackleak.c:30:46: error: implicit declaration of function 'stackleak_task_low_bound' [-Werror=implicit-function-declaration] | 30 | const unsigned long task_stack_low = stackleak_task_low_bound(current); | | ^~~~~~~~~~~~~~~~~~~~~~~~ | drivers/misc/lkdtm/stackleak.c:31:47: error: implicit declaration of function 'stackleak_task_high_bound'; did you mean 'stackleak_task_init'? [-Werror=implicit-function-declaration] | 31 | const unsigned long task_stack_high = stackleak_task_high_bound(current); | | ^~~~~~~~~~~~~~~~~~~~~~~~~ | | stackleak_task_init | drivers/misc/lkdtm/stackleak.c:33:48: error: 'struct task_struct' has no member named 'lowest_stack' | 33 | const unsigned long lowest_sp = current->lowest_stack; | | ^~ | drivers/misc/lkdtm/stackleak.c:74:23: error: implicit declaration of function 'stackleak_find_top_of_poison' [-Werror=implicit-function-declaration] | 74 | poison_high = stackleak_find_top_of_poison(task_stack_low, untracked_high); | | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~ This patch fixes the issue by not compiling the body of the test when CONFIG_GCC_PLUGIN_STACKLEAK=n, and replacing this with an unconditional XFAIL message. This means the pr_expected_config() in check_stackleak_irqoff() is redundant, and so it is removed. Where an architecture does not support stackleak, the test will log: | # echo STACKLEAK_ERASING > /sys/kernel/debug/provoke-crash/DIRECT | lkdtm: Performing direct entry STACKLEAK_ERASING | lkdtm: XFAIL: stackleak is not supported on this arch (HAVE_ARCH_STACKLEAK=n) Where an architectures does support stackleak, but this has not been compiled in, the test will log: | # echo STACKLEAK_ERASING > /sys/kernel/debug/provoke-crash/DIRECT | lkdtm: Performing direct entry STACKLEAK_ERASING | lkdtm: XFAIL: stackleak is not enabled (CONFIG_GCC_PLUGIN_STACKLEAK=n) Where stackleak has been compiled in, the test behaves as usual: | # echo STACKLEAK_ERASING > /sys/kernel/debug/provoke-crash/DIRECT | lkdtm: Performing direct entry STACKLEAK_ERASING | lkdtm: stackleak stack usage: | high offset: 336 bytes | current: 688 bytes | lowest: 1232 bytes | tracked: 1232 bytes | untracked: 672 bytes | poisoned: 14136 bytes | low offset: 8 bytes | lkdtm: OK: the rest of the thread stack is properly erased Fixes: f4cfacd92972cc44 ("lkdtm/stackleak: rework boundary management") Signed-off-by: Mark Rutland Cc: Alexander Popov Cc: Kees Cook Signed-off-by: Kees Cook Link: https://lore.kernel.org/r/20220506121145.1162908-1-mark.rutland@arm.com --- drivers/misc/lkdtm/stackleak.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/drivers/misc/lkdtm/stackleak.c b/drivers/misc/lkdtm/stackleak.c index 52800583fd05..82369c6f889e 100644 --- a/drivers/misc/lkdtm/stackleak.c +++ b/drivers/misc/lkdtm/stackleak.c @@ -11,6 +11,7 @@ #include "lkdtm.h" #include +#if defined(CONFIG_GCC_PLUGIN_STACKLEAK) /* * Check that stackleak tracks the lowest stack pointer and erases the stack * below this as expected. @@ -109,7 +110,6 @@ static void noinstr check_stackleak_irqoff(void) out: if (test_failed) { pr_err("FAIL: the thread stack is NOT properly erased!\n"); - pr_expected_config(CONFIG_GCC_PLUGIN_STACKLEAK); } else { pr_info("OK: the rest of the thread stack is properly erased\n"); } @@ -123,3 +123,13 @@ void lkdtm_STACKLEAK_ERASING(void) check_stackleak_irqoff(); local_irq_restore(flags); } +#else /* defined(CONFIG_GCC_PLUGIN_STACKLEAK) */ +void lkdtm_STACKLEAK_ERASING(void) +{ + if (IS_ENABLED(CONFIG_HAVE_ARCH_STACKLEAK)) { + pr_err("XFAIL: stackleak is not enabled (CONFIG_GCC_PLUGIN_STACKLEAK=n)\n"); + } else { + pr_err("XFAIL: stackleak is not supported on this arch (HAVE_ARCH_STACKLEAK=n)\n"); + } +} +#endif /* defined(CONFIG_GCC_PLUGIN_STACKLEAK) */