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Re: [PATCH 1/4] x86/entry: Work around Clang __bdos() bug
- To: Kees Cook <keescook@xxxxxxxxxxxx>, linux-hardening@xxxxxxxxxxxxxxx
- From: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
- Date: Tue, 20 Sep 2022 20:07:09 -0400
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- Cc: Juergen Gross <jgross@xxxxxxxx>, Nathan Chancellor <nathan@xxxxxxxxxx>, Nick Desaulniers <ndesaulniers@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, llvm@xxxxxxxxxxxxxxx, Siddhesh Poyarekar <siddhesh@xxxxxxxxxx>, Arnd Bergmann <arnd@xxxxxxxx>, Tom Rix <trix@xxxxxxxxxx>, Miguel Ojeda <ojeda@xxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx
- Delivery-date: Wed, 21 Sep 2022 00:07:52 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 9/20/22 3:21 PM, Kees Cook wrote:
After expanding bounds checking to use __builtin_dynamic_object_size(),
Clang produces a false positive when building with CONFIG_FORTIFY_SOURCE=y
and CONFIG_UBSAN_BOUNDS=y when operating on an array with a dynamic
offset. Work around this by using a direct assignment of an empty
instance. Avoids this warning:
../include/linux/fortify-string.h:309:4: warning: call to
__write_overflow_field declared with 'warn
ing' attribute: detected write beyond size of field (1st parameter); maybe use
struct_group()? [-Wat
tribute-warning]
__write_overflow_field(p_size_field, size);
^
which was isolated to the memset() call in xen_load_idt().
Note that this looks very much like another bug that was worked around:
https://github.com/ClangBuiltLinux/linux/issues/1592
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: Nathan Chancellor <nathan@xxxxxxxxxx>
Cc: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
Cc: llvm@xxxxxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
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