diff mbox series

[1/4] x86/entry: Work around Clang __bdos() bug

Message ID 20220920192202.190793-2-keescook@chromium.org (mailing list archive)
State Mainlined
Commit 3e1730842f142add55dc658929221521a9ea62b6
Headers show
Series fortify: Use __builtin_dynamic_object_size() when available | expand

Commit Message

Kees Cook Sept. 20, 2022, 7:21 p.m. UTC
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@suse.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: xen-devel@lists.xenproject.org
Cc: llvm@lists.linux.dev
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 arch/x86/xen/enlighten_pv.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Comments

Boris Ostrovsky Sept. 21, 2022, 12:07 a.m. UTC | #1
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@suse.com>
> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> Cc: Nathan Chancellor <nathan@kernel.org>
> Cc: Nick Desaulniers <ndesaulniers@google.com>
> Cc: xen-devel@lists.xenproject.org
> Cc: llvm@lists.linux.dev
> Signed-off-by: Kees Cook <keescook@chromium.org>


Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
diff mbox series

Patch

diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index 0ed2e487a693..9b1a58dda935 100644
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -765,6 +765,7 @@  static void xen_load_idt(const struct desc_ptr *desc)
 {
 	static DEFINE_SPINLOCK(lock);
 	static struct trap_info traps[257];
+	static const struct trap_info zero = { };
 	unsigned out;
 
 	trace_xen_cpu_load_idt(desc);
@@ -774,7 +775,7 @@  static void xen_load_idt(const struct desc_ptr *desc)
 	memcpy(this_cpu_ptr(&idt_desc), desc, sizeof(idt_desc));
 
 	out = xen_convert_trap_info(desc, traps, false);
-	memset(&traps[out], 0, sizeof(traps[0]));
+	traps[out] = zero;
 
 	xen_mc_flush();
 	if (HYPERVISOR_set_trap_table(traps))