linux-kernel - [PATCH v3] x86: disable non-instrumented version of copy

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Message-ID: <1a817eb5-7cd8-44d6-b409-b3bc3f377cb9@I-love.SAKURA.ne.jp>
Date: Sat, 2 Mar 2024 07:41:09 +0900
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To: LKML <linux-kernel@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH v3] x86: disable non-instrumented version of copy_page when
 KMSAN is enabled

Commit afb2d666d025 ("zsmalloc: use copy_page for full page copy") caused
a false-positive KMSAN warning. Implement copy_page() using memcpy() when
KMSAN is enabled.

  BUG: KMSAN: use-after-free in obj_malloc+0x6cc/0x7b0
  Uninit was stored to memory at:
   obj_malloc+0x70a/0x7b0
  Uninit was created at:
   free_unref_page_prepare+0x130/0xfc0

Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
---
Changes in v3:
  Update description/comment and use include file, suggested by
  Thomas Gleixner.
  
 arch/x86/include/asm/page_64.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/arch/x86/include/asm/page_64.h b/arch/x86/include/asm/page_64.h
index cc6b8e087192..98a71727dbac 100644
--- a/arch/x86/include/asm/page_64.h
+++ b/arch/x86/include/asm/page_64.h
@@ -9,6 +9,7 @@
 #include <asm/alternative.h>
 
 #include <linux/kmsan-checks.h>
+#include <linux/string.h>
 
 /* duplicated to the one in bootmem.h */
 extern unsigned long max_pfn;
@@ -58,7 +59,18 @@ static inline void clear_page(void *page)
 			   : "cc", "memory", "rax", "rcx");
 }
 
+#ifdef CONFIG_KMSAN
+/*
+ * The assembly version of copy_page() is not instrumented and
+ * therefore breaks KMSAN. Fall back to memcpy.
+ */
+static inline void copy_page(void *to, void *from)
+{
+	memcpy(to, from, PAGE_SIZE);
+}
+#else
 void copy_page(void *to, void *from);
+#endif
 
 #ifdef CONFIG_X86_5LEVEL
 /*
-- 
2.34.1