x86/uaccess: Dont leak the AC flag into __put_user() argument evaluation
The __put_user() macro evaluates it's @ptr argument inside the __uaccess_begin() / __uaccess_end() region. While this would normally not be expected to be an issue, an UBSAN bug (it ignored -fwrapv, fixed in GCC 8+) would transform the @ptr evaluation for: drivers/gpu/drm/i915/i915_gem_execbuffer.c: if (unlikely(__put_user(offset, &urelocs[r-stack].presumed_offset))) { into a signed-overflow-UB check and trigger the objtool AC validation. Finish this commit:2a418cf3f5
("x86/uaccess: Don't leak the AC flag into __put_user() value evaluation") and explicitly evaluate all 3 arguments early. Reported-by: Randy Dunlap <rdunlap@infradead.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Randy Dunlap <rdunlap@infradead.org> # build-tested Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: luto@kernel.org Fixes:2a418cf3f5
("x86/uaccess: Don't leak the AC flag into __put_user() value evaluation") Link: http://lkml.kernel.org/r/20190424072208.695962771@infradead.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
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@ -427,10 +427,11 @@ do { \
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({ \
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__label__ __pu_label; \
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int __pu_err = -EFAULT; \
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__typeof__(*(ptr)) __pu_val; \
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__pu_val = x; \
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__typeof__(*(ptr)) __pu_val = (x); \
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__typeof__(ptr) __pu_ptr = (ptr); \
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__typeof__(size) __pu_size = (size); \
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__uaccess_begin(); \
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__put_user_size(__pu_val, (ptr), (size), __pu_label); \
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__put_user_size(__pu_val, __pu_ptr, __pu_size, __pu_label); \
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__pu_err = 0; \
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__pu_label: \
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__uaccess_end(); \
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