From 73ab4a3509e6b8f93b87398db2aaabd3c9cbe487 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Wed, 18 Aug 2021 08:03:08 -0700 Subject: 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 Signed-off-by: Sean Christopherson Link: https://lore.kernel.org/lkml/YR0jIEzEcUom/7rd@google.com Signed-off-by: Kees Cook --- arch/x86/kvm/emulate.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) (limited to 'arch/x86/kvm/emulate.c') 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; -- cgit