[PATCH] x86/alternatives: Use C int3 selftest but disable KASAN

From: Kees Cook <keescook@chromium.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Sami Tolvanen <samitolvanen@google.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	linux-kernel@vger.kernel.org
Subject: [PATCH] x86/alternatives: Use C int3 selftest but disable KASAN
Date: Mon, 11 Nov 2019 13:51:16 -0800	[thread overview]
Message-ID: <201911111348.7A0A6C3AFD@keescook> (raw)

Instead of using inline asm for the int3 selftest (which confuses the
Clang's ThinLTO pass), this restores the C function but disables KASAN
(and tracing for good measure) to keep the things simple and avoid
unexpected side-effects. This attempts to keep the fix from commit
ecc606103837 ("x86/alternatives: Fix int3_emulate_call() selftest stack
corruption") without using inline asm.

Signed-off-by: Kees Cook <keescook@chromium.org>
---
 arch/x86/kernel/alternative.c | 21 ++++-----------------
 1 file changed, 4 insertions(+), 17 deletions(-)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 9d3a971ea364..efb5ef8a7885 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -625,23 +625,10 @@ extern struct paravirt_patch_site __start_parainstructions[],
  *
  * See entry_{32,64}.S for more details.
  */
-
-/*
- * We define the int3_magic() function in assembly to control the calling
- * convention such that we can 'call' it from assembly.
- */
-
-extern void int3_magic(unsigned int *ptr); /* defined in asm */
-
-asm (
-"	.pushsection	.init.text, \"ax\", @progbits\n"
-"	.type		int3_magic, @function\n"
-"int3_magic:\n"
-"	movl	$1, (%" _ASM_ARG1 ")\n"
-"	ret\n"
-"	.size		int3_magic, .-int3_magic\n"
-"	.popsection\n"
-);
+static void __init __no_sanitize_address notrace int3_magic(unsigned int *ptr)
+{
+	*ptr = 1;
+}
 
 extern __initdata unsigned long int3_selftest_ip; /* defined in asm below */
 
-- 
2.17.1


-- 
Kees Cook
