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Subject[PATCH] lkdtm: hide stack overflow warning for corrupt-stack test
Date
After the latest change to make sure the compiler actually does a memset,
it is now smart enough to flag the stack overflow at compile time,
at least with gcc-7.0:

drivers/misc/lkdtm_bugs.c: In function 'lkdtm_CORRUPT_STACK':
drivers/misc/lkdtm_bugs.c:88:144: warning: 'memset' writing 64 bytes into a region of size 8 overflows the destination [-Wstringop-overflow=]

To outsmart the compiler again, this moves the memset into a noinline
function where (for now) it doesn't see that we intentionally write
broken code here.

Fixes: c55d240003ae ("lkdtm: Prevent the compiler from optimising lkdtm_CORRUPT_STACK()")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
drivers/misc/lkdtm_bugs.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/misc/lkdtm_bugs.c b/drivers/misc/lkdtm_bugs.c
index 91edd0b55e5c..bb3bb8ef5f44 100644
--- a/drivers/misc/lkdtm_bugs.c
+++ b/drivers/misc/lkdtm_bugs.c
@@ -80,12 +80,17 @@ void lkdtm_OVERFLOW(void)
(void) recursive_loop(recur_count);
}

+static noinline void __lkdtm_CORRUPT_STACK(void *stack)
+{
+ memset(stack, 'a', 64);
+}
+
noinline void lkdtm_CORRUPT_STACK(void)
{
/* Use default char array length that triggers stack protection. */
char data[8];
+ __lkdtm_CORRUPT_STACK(&data);

- memset((void *)data, 'a', 64);
pr_info("Corrupted stack with '%16s'...\n", data);
}

--
2.9.0
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