diff options
| author | Sean Christopherson <seanjc@google.com> | 2021-08-18 08:03:08 -0700 |
|---|---|---|
| committer | Kees Cook <keescook@chromium.org> | 2022-02-13 16:48:04 -0800 |
| commit | 73ab4a3509e6b8f93b87398db2aaabd3c9cbe487 (patch) | |
| tree | 1870f8db63e9f47f2d018f25951879ca3c0ce9fc /arch/x86/kvm/emulate.c | |
| parent | dfd42facf1e4ada021b939b4e19c935dcdd55566 (diff) | |
KVM: x86: Replace memset() "optimization" with normal per-field writes
Explicitly zero select fields in the emulator's decode cache instead of
zeroing the fields via a gross memset() that spans six fields. gcc and
clang are both clever enough to batch the first five fields into a single
quadword MOV, i.e. memset() and individually zeroing generate identical
code.
Removing the wart also prepares KVM for FORTIFY_SOURCE performing
compile-time and run-time field bounds checking for memset().
No functional change intended.
Reported-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/lkml/YR0jIEzEcUom/7rd@google.com
Signed-off-by: Kees Cook <keescook@chromium.org>
Diffstat (limited to 'arch/x86/kvm/emulate.c')
| -rw-r--r-- | arch/x86/kvm/emulate.c | 9 |
1 files changed, 7 insertions, 2 deletions
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c index 5719d8cfdbd9..6b820cc2b51b 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -5380,8 +5380,13 @@ 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); + /* Clear fields that are set conditionally but read without a guard. */ + ctxt->rip_relative = false; + ctxt->rex_prefix = 0; + ctxt->lock_prefix = 0; + ctxt->rep_prefix = 0; + ctxt->regs_valid = 0; + ctxt->regs_dirty = 0; ctxt->io_read.pos = 0; ctxt->io_read.end = 0; |