Commit 3e173084 authored Sep 19, 2022 by Kees Cook

x86/entry: Work around Clang __bdos() bug

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: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: x86@kernel.org
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: xen-devel@lists.xenproject.org
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Link: https://lore.kernel.org/lkml/41527d69-e8ab-3f86-ff37-6b298c01d5bc@oracle.com


Signed-off-by: Kees Cook <keescook@chromium.org>

parent 1b64daf4

arch/x86/xen/enlighten_pv.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -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))