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    Subject[PATCH 6.0 676/862] x86/entry: Work around Clang __bdos() bug
    Date
    From: Kees Cook <keescook@chromium.org>

    [ Upstream commit 3e1730842f142add55dc658929221521a9ea62b6 ]

    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>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    arch/x86/xen/enlighten_pv.c | 3 ++-
    1 file changed, 2 insertions(+), 1 deletion(-)

    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))
    --
    2.35.1


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