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lkdtm: Emit an indirect call for CFI tests

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Clang can convert the indirect calls in lkdtm_CFI_FORWARD_PROTO into
direct calls. Move the call into a noinline function that accepts the
target address as an argument to ensure the compiler actually emits an
indirect call instead.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Kees Cook <keescook@chromium.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Acked-by: Kees Cook <keescook@chromium.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220908215504.3686827-8-samitolvanen@google.com
This commit is contained in:
Sami Tolvanen 2022-09-08 14:54:49 -07:00 • committed by Kees Cook
parent e84e008e7b
commit cf90d03835
1 changed files with 9 additions and 6 deletions
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15
drivers/misc/lkdtm/cfi.c
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@ -20,6 +20,13 @@ static noinline int lkdtm_increment_int(int *counter)
return *counter; return *counter;
} }
/* Don't allow the compiler to inline the calls. */
static noinline void lkdtm_indirect_call(void (*func)(int *))
{
func(&called_count);
}
/* /*
* This tries to call an indirect function with a mismatched prototype. * This tries to call an indirect function with a mismatched prototype.
*/ */
@ -29,15 +36,11 @@ static void lkdtm_CFI_FORWARD_PROTO(void)
* Matches lkdtm_increment_void()'s prototype, but not * Matches lkdtm_increment_void()'s prototype, but not
* lkdtm_increment_int()'s prototype. * lkdtm_increment_int()'s prototype.
*/ */
void (*func)(int *);
pr_info("Calling matched prototype ...\n"); pr_info("Calling matched prototype ...\n");
func = lkdtm_increment_void; lkdtm_indirect_call(lkdtm_increment_void);
func(&called_count);
pr_info("Calling mismatched prototype ...\n"); pr_info("Calling mismatched prototype ...\n");
func = (void *)lkdtm_increment_int; lkdtm_indirect_call((void *)lkdtm_increment_int);
func(&called_count);
pr_err("FAIL: survived mismatched prototype function call!\n"); pr_err("FAIL: survived mismatched prototype function call!\n");
pr_expected_config(CONFIG_CFI_CLANG); pr_expected_config(CONFIG_CFI_CLANG);