linux-kernel - [PATCH] string: uninline memcpy_and

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Message-Id: <20211102043024.449478-1-linux@roeck-us.net>
Date:   Mon,  1 Nov 2021 21:30:24 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Andy Shevchenko <andy@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>
Subject: [PATCH] string: uninline memcpy_and_pad

When building m68k:allmodconfig, recent versions of gcc generate the
following error if the length of UTS_RELEASE is less than 8 bytes.

In function 'memcpy_and_pad',
    inlined from 'nvmet_execute_disc_identify' at
    	drivers/nvme/target/discovery.c:268:2:
arch/m68k/include/asm/string.h:72:25: error:
	'__builtin_memcpy' reading 8 bytes from a region of size 7

Discussions around the problem suggest that this only happens if an
architecture does not provide strlen(), if -ffreestanding is provided as
compiler option, and if CONFIG_FORTIFY_SOURCE=n. All of this is the case
for m68k. The exact reasons are unknown, but seem to be related to the
ability of the compiler to evaluate the return value of strlen() and
the resulting execution flow in memcpy_and_pad(). It would be possible
to work around the problem by using sizeof(UTS_RELEASE) instead of
strlen(UTS_RELEASE), but that would only postpone the problem until the
function is called in a similar way. Uninline memcpy_and_pad() instead
to solve the problem for good.

Suggested-by: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Geert Uytterhoeven <geert@...ux-m68k.org>
Signed-off-by: Guenter Roeck <linux@...ck-us.net>
---
 include/linux/string.h | 19 ++-----------------
 lib/string.c           | 19 +++++++++++++++++++
 2 files changed, 21 insertions(+), 17 deletions(-)

diff --git a/include/linux/string.h b/include/linux/string.h
index 5e96d656be7a..d68097b4f600 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -262,23 +262,8 @@ void __write_overflow(void) __compiletime_error("detected write beyond size of o
 #include <linux/fortify-string.h>
 #endif
 
-/**
- * memcpy_and_pad - Copy one buffer to another with padding
- * @dest: Where to copy to
- * @dest_len: The destination buffer size
- * @src: Where to copy from
- * @count: The number of bytes to copy
- * @pad: Character to use for padding if space is left in destination.
- */
-static inline void memcpy_and_pad(void *dest, size_t dest_len,
-				  const void *src, size_t count, int pad)
-{
-	if (dest_len > count) {
-		memcpy(dest, src, count);
-		memset(dest + count, pad,  dest_len - count);
-	} else
-		memcpy(dest, src, dest_len);
-}
+void memcpy_and_pad(void *dest, size_t dest_len, const void *src, size_t count,
+		    int pad);
 
 /**
  * str_has_prefix - Test if a string has a given prefix
diff --git a/lib/string.c b/lib/string.c
index b2de45a581f4..ff13d6d77a05 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -1165,3 +1165,22 @@ void fortify_panic(const char *name)
 	BUG();
 }
 EXPORT_SYMBOL(fortify_panic);
+
+/**
+ * memcpy_and_pad - Copy one buffer to another with padding
+ * @dest: Where to copy to
+ * @dest_len: The destination buffer size
+ * @src: Where to copy from
+ * @count: The number of bytes to copy
+ * @pad: Character to use for padding if space is left in destination.
+ */
+void memcpy_and_pad(void *dest, size_t dest_len, const void *src, size_t count,
+		    int pad)
+{
+	if (dest_len > count) {
+		memcpy(dest, src, count);
+		memset(dest + count, pad,  dest_len - count);
+	} else
+		memcpy(dest, src, dest_len);
+}
+EXPORT_SYMBOL(memcpy_and_pad);
-- 
2.33.0