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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 <mark.rutland@arm.com>
Cc: Alexander Popov <alex.popov@linux.com>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220506121145.1162908-1-mark.rutland@arm.com
This commit is contained in:
Mark Rutland 2022-05-06 13:11:45 +01:00 committed by Kees Cook
parent 88959a39a1
commit 8c6a490e40
1 changed files with 11 additions and 1 deletions
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12
drivers/misc/lkdtm/stackleak.c
View File

@ -11,6 +11,7 @@
#include "lkdtm.h"
#include <linux/stackleak.h>
#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) */