From 719d5a9b2487e0562f178f61e323c3dc18a8b200 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Thu, 19 Jun 2014 11:37:06 +0200 Subject: [PATCH] KVM: x86: ensure emulator fetches do not span multiple pages When the CS base is not page-aligned, the linear address of the code could get close to the page boundary (e.g. 0x...ffe) even if the EIP value is not. So we need to first linearize the address, and only then compute the number of valid bytes that can be fetched. This happens relatively often when executing real mode code. Signed-off-by: Paolo Bonzini --- arch/x86/kvm/emulate.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-) diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c index c16314807756..6a1d60956d63 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -711,14 +711,18 @@ static int segmented_read_std(struct x86_emulate_ctxt *ctxt, static int __do_insn_fetch_bytes(struct x86_emulate_ctxt *ctxt, int op_size) { int rc; - int size; + unsigned size; unsigned long linear; int cur_size = ctxt->fetch.end - ctxt->fetch.data; struct segmented_address addr = { .seg = VCPU_SREG_CS, .ea = ctxt->eip + cur_size }; - size = min(15UL ^ cur_size, - PAGE_SIZE - offset_in_page(addr.ea)); + size = 15UL ^ cur_size; + rc = __linearize(ctxt, addr, size, false, true, &linear); + if (unlikely(rc != X86EMUL_CONTINUE)) + return rc; + + size = min_t(unsigned, size, PAGE_SIZE - offset_in_page(linear)); /* * One instruction can only straddle two pages, @@ -728,9 +732,6 @@ static int __do_insn_fetch_bytes(struct x86_emulate_ctxt *ctxt, int op_size) */ if (unlikely(size < op_size)) return X86EMUL_UNHANDLEABLE; - rc = __linearize(ctxt, addr, size, false, true, &linear); - if (unlikely(rc != X86EMUL_CONTINUE)) - return rc; rc = ctxt->ops->fetch(ctxt, linear, ctxt->fetch.end, size, &ctxt->exception); if (unlikely(rc != X86EMUL_CONTINUE)) -- 2.20.1