From fe360c90ea13f309ef78810f1a2b92f2ae3b30b8 Mon Sep 17 00:00:00 2001 From: Jan Beulich Date: Thu, 29 Oct 2015 13:35:07 +0100 Subject: [PATCH] x86: guard against undue super page PTE creation MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit When optional super page support got added (commit bd1cd81d64 "x86: PV support for hugepages"), two adjustments were missed: mod_l2_entry() needs to consider the PSE and RW bits when deciding whether to use the fast path, and the PSE bit must not be removed from L2_DISALLOW_MASK unconditionally. This is CVE-2015-7835 / XSA-148. Reported-by: "栾尚聪(好风)" Signed-off-by: Jan Beulich Reviewed-by: Tim Deegan --- xen/arch/x86/mm.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c index 87634146a2..b65c3a51e2 100644 --- a/xen/arch/x86/mm.c +++ b/xen/arch/x86/mm.c @@ -160,7 +160,10 @@ static void put_superpage(unsigned long mfn); static uint32_t base_disallow_mask; /* Global bit is allowed to be set on L1 PTEs. Intended for user mappings. */ #define L1_DISALLOW_MASK ((base_disallow_mask | _PAGE_GNTTAB) & ~_PAGE_GLOBAL) -#define L2_DISALLOW_MASK (base_disallow_mask & ~_PAGE_PSE) + +#define L2_DISALLOW_MASK (unlikely(opt_allow_superpage) \ + ? base_disallow_mask & ~_PAGE_PSE \ + : base_disallow_mask) #define l3_disallow_mask(d) (!is_pv_32bit_domain(d) ? \ base_disallow_mask : 0xFFFFF198U) @@ -1839,7 +1842,10 @@ static int mod_l2_entry(l2_pgentry_t *pl2e, } /* Fast path for identical mapping and presence. */ - if ( !l2e_has_changed(ol2e, nl2e, _PAGE_PRESENT) ) + if ( !l2e_has_changed(ol2e, nl2e, + unlikely(opt_allow_superpage) + ? _PAGE_PSE | _PAGE_RW | _PAGE_PRESENT + : _PAGE_PRESENT) ) { adjust_guest_l2e(nl2e, d); if ( UPDATE_ENTRY(l2, pl2e, ol2e, nl2e, pfn, vcpu, preserve_ad) ) -- 2.30.2