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SUSE:SLE-12-SP1:Update
xen.8426
xsa264.patch
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File xsa264.patch of Package xen.8426
From: Jan Beulich <jbeulich@suse.com> Subject: x86/mm: don't bypass preemption checks While unlikely, it is not impossible for a multi-vCPU guest to leverage bypasses of preemption checks to drive Xen into an unbounded loop. This is XSA-264. Signed-off-by: Jan Beulich <jbeulich@suse.com> Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com> --- a/xen/arch/x86/mm.c +++ b/xen/arch/x86/mm.c @@ -2446,7 +2446,7 @@ static int _put_page_type(struct page_in nx = x & ~(PGT_validated|PGT_partial); if ( unlikely((y = cmpxchg(&page->u.inuse.type_info, x, nx)) != x) ) - continue; + goto maybe_preempt; /* We cleared the 'valid bit' so we do the clean up. */ rc = _put_final_page_type(page, x, preemptible, ptpg); ptpg = NULL; @@ -2481,12 +2481,13 @@ static int _put_page_type(struct page_in */ cpu_relax(); y = page->u.inuse.type_info; - continue; + goto maybe_preempt; } if ( likely((y = cmpxchg(&page->u.inuse.type_info, x, nx)) == x) ) break; + maybe_preempt: if ( preemptible && hypercall_preempt_check() ) return -EINTR; } @@ -2590,12 +2591,11 @@ static int __get_page_type(struct page_i if ( !(x & PGT_partial) ) { /* Someone else is updating validation of this page. Wait... */ - while ( (y = page->u.inuse.type_info) == x ) - { + do { if ( preemptible && hypercall_preempt_check() ) return -EINTR; cpu_relax(); - } + } while ( (y = page->u.inuse.type_info) == x ); continue; } /* Type ref count was left at 1 when PGT_partial got set. */
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