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Message-ID: <3b7dbd88-0861-4638-b2d2-911c97a4cadf@I-love.SAKURA.ne.jp>
Date: Sat, 2 Mar 2024 07:52:23 +0900
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To: LKML <linux-kernel@vger.kernel.org>,
        the arch/x86 maintainers <x86@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "H. Peter Anvin" <hpa@zytor.com>
From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Subject: [PATCH v2] x86: disable non-instrumented version of copy_mc when
 KMSAN is enabled
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dump_emit_page() caused a false-positive KMSAN warning, for
memcpy_from_iter_mc() is called via iterate_bvec() by setting "struct
iov_iter"->copy_mc to true.

Fallback to memcpy()/copy_user_generic() when KMSAN is enabled.

Reported-by: syzbot <syzbot+d7521c1e3841ed075a42@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=d7521c1e3841ed075a42
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Tested-by: syzbot <syzbot+d7521c1e3841ed075a42@syzkaller.appspotmail.com>
Reviewed-by: Alexander Potapenko <glider@google.com>
---
Changes in v2:
  Update description.

 arch/x86/lib/copy_mc.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/lib/copy_mc.c b/arch/x86/lib/copy_mc.c
index 6e8b7e600def..c6a0b8dbf58d 100644
--- a/arch/x86/lib/copy_mc.c
+++ b/arch/x86/lib/copy_mc.c
@@ -61,9 +61,9 @@ unsigned long copy_mc_enhanced_fast_string(void *dst, const void *src, unsigned
  */
 unsigned long __must_check copy_mc_to_kernel(void *dst, const void *src, unsigned len)
 {
-	if (copy_mc_fragile_enabled)
+	if (!IS_ENABLED(CONFIG_KMSAN) && copy_mc_fragile_enabled)
 		return copy_mc_fragile(dst, src, len);
-	if (static_cpu_has(X86_FEATURE_ERMS))
+	if (!IS_ENABLED(CONFIG_KMSAN) && static_cpu_has(X86_FEATURE_ERMS))
 		return copy_mc_enhanced_fast_string(dst, src, len);
 	memcpy(dst, src, len);
 	return 0;
@@ -74,14 +74,14 @@ unsigned long __must_check copy_mc_to_user(void __user *dst, const void *src, un
 {
 	unsigned long ret;
 
-	if (copy_mc_fragile_enabled) {
+	if (!IS_ENABLED(CONFIG_KMSAN) && copy_mc_fragile_enabled) {
 		__uaccess_begin();
 		ret = copy_mc_fragile((__force void *)dst, src, len);
 		__uaccess_end();
 		return ret;
 	}
 
-	if (static_cpu_has(X86_FEATURE_ERMS)) {
+	if (!IS_ENABLED(CONFIG_KMSAN) && static_cpu_has(X86_FEATURE_ERMS)) {
 		__uaccess_begin();
 		ret = copy_mc_enhanced_fast_string((__force void *)dst, src, len);
 		__uaccess_end();
-- 
2.34.1