linux-kernel - [PATCH] KVM: emulator: Handle wraparound in (cs

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Date:	Wed, 13 Apr 2011 11:44:13 -0400
From:	Nelson Elhage <nelhage@...lice.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	Nelson Elhage <nelhage@...lice.com>
Subject: [PATCH] KVM: emulator: Handle wraparound in (cs_base + offset) when fetching.

Currently, setting a large (i.e. negative) base address for %cs does not work on
a 64-bit host. The "JOS" teaching operating system, used by MIT and other
universities, relies on such segments while bootstrapping its way to full
virtual memory management.

Signed-off-by: Nelson Elhage <nelhage@...lice.com>
---
 arch/x86/kvm/emulate.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 0ad47b8..54e84b2 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -505,9 +505,12 @@ static int do_fetch_insn_byte(struct x86_emulate_ctxt *ctxt,
 	int size, cur_size;
 
 	if (eip == fc->end) {
+		unsigned long linear = eip + ctxt->cs_base;
+		if (ctxt->mode != X86EMUL_MODE_PROT64)
+			linear &= (u32)-1;
 		cur_size = fc->end - fc->start;
 		size = min(15UL - cur_size, PAGE_SIZE - offset_in_page(eip));
-		rc = ops->fetch(ctxt->cs_base + eip, fc->data + cur_size,
+		rc = ops->fetch(linear, fc->data + cur_size,
 				size, ctxt->vcpu, &ctxt->exception);
 		if (rc != X86EMUL_CONTINUE)
 			return rc;
-- 
1.7.2.43.g36c08.dirty

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/