[PATCH v2 53/63] KVM: x86: Use struct_group() to zero decode cache

Kees Cook
2021-08-18T06:15:52Z

In preparation for FORTIFY_SOURCE performing compile-time and run-time
field bounds checking for memset(), avoid intentionally writing across
neighboring fields.

Add struct_group() to mark region of struct x86_emulate_ctxt that should
be initialized to zero.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Wanpeng Li <wanpengli@tencent.com>
Cc: Jim Mattson <jmattson@google.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: x86@kernel.org
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: kvm@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
arch/x86/kvm/emulate.c | 3 +--
arch/x86/kvm/kvm_emulate.h | 19 +++++++++++--------
2 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 2837110e66ed..2608a047e769 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -5377,8 +5377,7 @@ static int fastop(struct x86_emulate_ctxt *ctxt, fastop_t fop)

void init_decode_cache(struct x86_emulate_ctxt *ctxt)
{
- memset(&ctxt->rip_relative, 0,
- (void *)&ctxt->modrm - (void *)&ctxt->rip_relative);
+ memset(&ctxt->decode_cache, 0, sizeof(ctxt->decode_cache));

ctxt->io_read.pos = 0;
ctxt->io_read.end = 0;
diff --git a/arch/x86/kvm/kvm_emulate.h b/arch/x86/kvm/kvm_emulate.h
index 68b420289d7e..9b8afcb8ad39 100644
--- a/arch/x86/kvm/kvm_emulate.h
+++ b/arch/x86/kvm/kvm_emulate.h
@@ -341,14 +341,17 @@ struct x86_emulate_ctxt {
* the rest are initialized unconditionally in x86_decode_insn
* or elsewhere
*/
- bool rip_relative;
- u8 rex_prefix;
- u8 lock_prefix;
- u8 rep_prefix;
- /* bitmaps of registers in _regs[] that can be read */
- u32 regs_valid;
- /* bitmaps of registers in _regs[] that have been written */
- u32 regs_dirty;
+ struct_group(decode_cache,
+ bool rip_relative;
+ u8 rex_prefix;
+ u8 lock_prefix;
+ u8 rep_prefix;
+ /* bitmaps of registers in _regs[] that can be read */
+ u32 regs_valid;
+ /* bitmaps of registers in _regs[] that have been written */
+ u32 regs_dirty;
+ );
+
/* modrm */
u8 modrm;
u8 modrm_mod;
--
2.30.2