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ARM: 9321/1: memset: cast the constant byte to unsigned char
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[ Upstream commit c0e8246 ]

memset() description in ISO/IEC 9899:1999 (and elsewhere) says:

	The memset function copies the value of c (converted to an
	unsigned char) into each of the first n characters of the
	object pointed to by s.

The kernel's arm32 memset does not cast c to unsigned char. This results
in the following code to produce erroneous output:

	char a[128];
	memset(a, -128, sizeof(a));

This is because gcc will generally emit the following code before
it calls memset() :

	mov   r0, r7
	mvn   r1, #127        ; 0x7f
	bl    00000000 <memset>

r1 ends up with 0xffffff80 before being used by memset() and the
'a' array will have -128 once in every four bytes while the other
bytes will be set incorrectly to -1 like this (printing the first
8 bytes) :

	test_module: -128 -1 -1 -1
	test_module: -1 -1 -1 -128

The change here is to 'and' r1 with 255 before it is used.

Fixes: 1da177e ("Linux-2.6.12-rc2")
Reviewed-by: Ard Biesheuvel <[email protected]>
Reviewed-by: Linus Walleij <[email protected]>
Signed-off-by: Kursad Oney <[email protected]>
Signed-off-by: Russell King (Oracle) <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>
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Kursad Oney authored and gregkh committed Nov 20, 2023
1 parent 0a7f923 commit 242ba2e
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1 change: 1 addition & 0 deletions arch/arm/lib/memset.S
Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,7 @@ ENTRY(__memset)
ENTRY(mmioset)
WEAK(memset)
UNWIND( .fnstart )
and r1, r1, #255 @ cast to unsigned char
ands r3, r0, #3 @ 1 unaligned?
mov ip, r0 @ preserve r0 as return value
bne 6f @ 1
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