On Tue, May 20, 2025 at 05:01:51PM +0300, Andy Shevchenko wrote:

On Mon, May 19, 2025 at 12:15:30PM -0700, Kees Cook wrote:

quoted

On Mon, May 19, 2025 at 08:41:17PM +0200, Mickaël Salaün wrote:

...

quoted

quoted

From 6fbf66fdfd0a7dac809b77faafdd72c60112bb8d Mon Sep 17 00:00:00 2001

From: Kees Cook <kees@kernel.org>
Date: Mon, 19 May 2025 11:52:06 -0700
Subject: [PATCH] string.h: Provide basic sanity checks for fallback memcpy()
MIME-Version: 1.0
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Instead of defining memcpy() in terms of __builtin_memcpy() deep
in arch/x86/include/asm/string_32.h, notice that it is needed up in
the general string.h, as done with other common C String APIs. This
allows us to add basic sanity checking for pathological "size"
arguments to memcpy(). Besides the run-time checking benefit, this
avoids GCC trying to be very smart about value range tracking[1] when
CONFIG_PROFILE_ALL_BRANCHES=y but FORTIFY_SOURCE=n.

Link: https://lore.kernel.org/all/202505191117.C094A90F88@keescook/ (local) [1]
Reported-by: kernel test robot <redacted>
Closes: https://lore.kernel.org/all/202501040747.S3LYfvYq-lkp@intel.com/ (local)
Reported-by: Randy Dunlap <redacted>
Closes: https://lore.kernel.org/all/e3754f69-1dea-4542-8de0-a567a14fb95b@infradead.org/ (local)
Signed-off-by: Kees Cook <kees@kernel.org>
---
Cc: "Mickaël Salaün" <mic@digikod.net>
Cc: Thomas Gleixner <redacted>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: <x86@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Andy Shevchenko <andy@kernel.org>
Cc: Uros Bizjak <redacted>
Cc: <redacted>
---
 arch/x86/include/asm/string_32.h |  6 ------
 include/linux/string.h           | 13 +++++++++++++
 2 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/string_32.h b/arch/x86/include/asm/string_32.h
index e9cce169bb4c..74397c95fa37 100644
--- a/arch/x86/include/asm/string_32.h
+++ b/arch/x86/include/asm/string_32.h

@@ -145,12 +145,6 @@ static __always_inline void *__constant_memcpy(void *to, const void *from,
 #define __HAVE_ARCH_MEMCPY
 extern void *memcpy(void *, const void *, size_t);
 
-#ifndef CONFIG_FORTIFY_SOURCE
-
-#define memcpy(t, f, n) __builtin_memcpy(t, f, n)
-
-#endif /* !CONFIG_FORTIFY_SOURCE */
-
 #define __HAVE_ARCH_MEMMOVE
 void *memmove(void *dest, const void *src, size_t n);
 

diff --git a/include/linux/string.h b/include/linux/string.h
index 01621ad0f598..ffcee31a14f9 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h

@@ -3,6 +3,7 @@
 #define _LINUX_STRING_H_
 
 #include <linux/args.h>
+#include <linux/bug.h>

In case you are go with this change, please keep the headers in order.

quoted

 #include <linux/array_size.h>

(should be located here)

Oops, yes, that was my intent but I typoed my insert, it seems. Fixed
now; thanks!

-Kees

-- 
Kees Cook