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x86/uaccess: Zero the 8-byte get_range case on failure on 32-bit

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While zeroing the upper 32 bits of an 8-byte getuser on 32-bit x86 was
fixed by commit 8c860ed825 ("x86/uaccess: Fix missed zeroing of ia32 u64
get_user() range checking") it was broken again in commit 8a2462df15
("x86/uaccess: Improve the 8-byte getuser() case").

This is because the register which holds the upper 32 bits (%ecx) is being
cleared _after_ the check_range, so if the range check fails, %ecx is never
cleared.

This can be reproduced with:
./tools/testing/kunit/kunit.py run --arch i386 usercopy

Instead, clear %ecx _before_ check_range in the 8-byte case. This
reintroduces a bit of the ugliness we were trying to avoid by adding
another #ifndef CONFIG_X86_64, but at least keeps check_range from needing
a separate bad_get_user_8 jump.

Fixes: 8a2462df15 ("x86/uaccess: Improve the 8-byte getuser() case")
Signed-off-by: David Gow <davidgow@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/all/20240731073031.4045579-1-davidgow@google.com
This commit is contained in:
David Gow 2024-07-31 15:30:29 +08:00 committed by Thomas Gleixner
parent 3db03fb499
commit dd35a09332
1 changed files with 3 additions and 1 deletions
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4
arch/x86/lib/getuser.S
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@ -88,12 +88,14 @@ SYM_FUNC_END(__get_user_4)
EXPORT_SYMBOL(__get_user_4)
SYM_FUNC_START(__get_user_8)
#ifndef CONFIG_X86_64
xor %ecx,%ecx
#endif
check_range size=8
ASM_STAC
#ifdef CONFIG_X86_64
UACCESS movq (%_ASM_AX),%rdx
#else
xor %ecx,%ecx
UACCESS movl (%_ASM_AX),%edx
UACCESS movl 4(%_ASM_AX),%ecx
#endif