From 0771faba163769089c9f05f7f76b63e397677613 Mon Sep 17 00:00:00 2001 From: Matthew Daley Date: Thu, 10 Oct 2013 15:19:53 +0200 Subject: x86: check segment descriptor read result in 64-bit OUTS emulation When emulating such an operation from a 64-bit context (CS has long mode set), and the data segment is overridden to FS/GS, the result of reading the overridden segment's descriptor (read_descriptor) is not checked. If it fails, data_base is left uninitialized. This can lead to 8 bytes of Xen's stack being leaked to the guest (implicitly, i.e. via the address given in a #PF). Coverity-ID: 1055116 This is CVE-2013-4368 / XSA-67. Signed-off-by: Matthew Daley Fix formatting. Signed-off-by: Jan Beulich --- xen/arch/x86/traps.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c index 47c71b7689..4a0950280f 100644 --- a/xen/arch/x86/traps.c +++ b/xen/arch/x86/traps.c @@ -1986,10 +1986,10 @@ static int emulate_privileged_op(struct cpu_user_regs *regs) break; } } - else - read_descriptor(data_sel, v, regs, - &data_base, &data_limit, &ar, - 0); + else if ( !read_descriptor(data_sel, v, regs, + &data_base, &data_limit, &ar, 0) || + !(ar & _SEGMENT_S) || !(ar & _SEGMENT_P) ) + goto fail; data_limit = ~0UL; ar = _SEGMENT_WR|_SEGMENT_S|_SEGMENT_DPL|_SEGMENT_P; } -- cgit v1.2.3