linux-hardening - [PATCH 09/15] x86/alternatives: Use C int3 selftest but disable KASAN

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Date:   Fri, 16 Apr 2021 13:38:38 -0700
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     x86@...nel.org
Cc:     Kees Cook <keescook@...omium.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Sedat Dilek <sedat.dilek@...il.com>,
        linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com,
        Sami Tolvanen <samitolvanen@...gle.com>
Subject: [PATCH 09/15] x86/alternatives: Use C int3 selftest but disable KASAN

From: Kees Cook <keescook@...omium.org>

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@...omium.org>
Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
---
 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 6974b5174495..669a23454c09 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -496,23 +496,10 @@ 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 */
 
-- 
2.31.1.368.gbe11c130af-goog