[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [xen stable-4.14] x86/shadow: tolerate failure of sh_set_toplevel_shadow()
commit 0bab3abf73783da66af8cf7cf7aabb7d86caa035 Author: Jan Beulich <jbeulich@xxxxxxxx> AuthorDate: Tue Oct 11 15:35:43 2022 +0200 Commit: Jan Beulich <jbeulich@xxxxxxxx> CommitDate: Tue Oct 11 15:35:43 2022 +0200 x86/shadow: tolerate failure of sh_set_toplevel_shadow() Subsequently sh_set_toplevel_shadow() will be adjusted to install a blank entry in case prealloc fails. There are, in fact, pre-existing error paths which would put in place a blank entry. The 4- and 2-level code in sh_update_cr3(), however, assume the top level entry to be valid. Hence bail from the function in the unlikely event that it's not. Note that 3-level logic works differently: In particular a guest is free to supply a PDPTR pointing at 4 non-present (or otherwise deemed invalid) entries. The guest will crash, but we already cope with that. Really mfn_valid() is likely wrong to use in sh_set_toplevel_shadow(), and it should instead be !mfn_eq(gmfn, INVALID_MFN). Avoid such a change in security context, but add a respective assertion. This is part of CVE-2022-33746 / XSA-410. Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx> Acked-by: Tim Deegan <tim@xxxxxxx> Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx> master commit: eac000978c1feb5a9ee3236ab0c0da9a477e5336 master date: 2022-10-11 14:22:24 +0200 --- xen/arch/x86/mm/shadow/multi.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/xen/arch/x86/mm/shadow/multi.c b/xen/arch/x86/mm/shadow/multi.c index 99e410d999..c129b8103e 100644 --- a/xen/arch/x86/mm/shadow/multi.c +++ b/xen/arch/x86/mm/shadow/multi.c @@ -3854,6 +3854,7 @@ sh_set_toplevel_shadow(struct vcpu *v, /* Now figure out the new contents: is this a valid guest MFN? */ if ( !mfn_valid(gmfn) ) { + ASSERT(mfn_eq(gmfn, INVALID_MFN)); new_entry = pagetable_null(); goto install_new_entry; } @@ -4007,6 +4008,11 @@ sh_update_cr3(struct vcpu *v, int do_locking, bool noflush) if ( sh_remove_write_access(d, gmfn, 2, 0) != 0 ) guest_flush_tlb_mask(d, d->dirty_cpumask); sh_set_toplevel_shadow(v, 0, gmfn, SH_type_l2_shadow); + if ( unlikely(pagetable_is_null(v->arch.shadow_table[0])) ) + { + ASSERT(d->is_dying || d->is_shutting_down); + return; + } #elif GUEST_PAGING_LEVELS == 3 /* PAE guests have four shadow_table entries, based on the * current values of the guest's four l3es. */ @@ -4052,6 +4058,11 @@ sh_update_cr3(struct vcpu *v, int do_locking, bool noflush) if ( sh_remove_write_access(d, gmfn, 4, 0) != 0 ) guest_flush_tlb_mask(d, d->dirty_cpumask); sh_set_toplevel_shadow(v, 0, gmfn, SH_type_l4_shadow); + if ( unlikely(pagetable_is_null(v->arch.shadow_table[0])) ) + { + ASSERT(d->is_dying || d->is_shutting_down); + return; + } if ( !shadow_mode_external(d) && !is_pv_32bit_domain(d) ) { mfn_t smfn = pagetable_get_mfn(v->arch.shadow_table[0]); -- generated by git-patchbot for /home/xen/git/xen.git#stable-4.14
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