From 9c4f1b72571b215e80abf0490073438831dc785b Mon Sep 17 00:00:00 2001 From: Jan Beulich Date: Tue, 6 Jun 2017 14:36:41 +0200 Subject: [PATCH] x86/HVM: correct notion of new CPL in task switch emulation Commit aac1df3d03 ("x86/HVM: introduce hvm_get_cpl() and respective hook") went too far in one aspect: When emulating a task switch we really shouldn't be looking at what hvm_get_cpl() returns, as we're switching all segment registers. The issue manifests as a vmentry failure for 32bit VMs which use task gates to service interrupts/exceptions, in situations where delivering the event interrupts user code, and a privilege increase is required. However, instead of reverting the relevant parts of that commit, have the caller tell the segment loading function what the new CPL is. This at once fixes ES being loaded before CS so far having had its checks done against the old CPL. Reported-by: Andrew Cooper Signed-off-by: Jan Beulich Reviewed-by: Andrew Cooper Tested-by: Andrew Cooper --- xen/arch/x86/hvm/hvm.c | 23 ++++++++++++----------- 1 file changed, 12 insertions(+), 11 deletions(-) diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c index 273bcff9ba..4b772a5742 100644 --- a/xen/arch/x86/hvm/hvm.c +++ b/xen/arch/x86/hvm/hvm.c @@ -2616,11 +2616,11 @@ static void hvm_unmap_entry(void *p) } static int hvm_load_segment_selector( - enum x86_segment seg, uint16_t sel, unsigned int eflags) + enum x86_segment seg, uint16_t sel, unsigned int cpl, unsigned int eflags) { struct segment_register desctab, segr; struct desc_struct *pdesc, desc; - u8 dpl, rpl, cpl; + u8 dpl, rpl; bool_t writable; int fault_type = TRAP_invalid_tss; struct vcpu *v = current; @@ -2674,7 +2674,6 @@ static int hvm_load_segment_selector( dpl = (desc.b >> 13) & 3; rpl = sel & 3; - cpl = hvm_get_cpl(v); switch ( seg ) { @@ -2804,7 +2803,7 @@ void hvm_task_switch( struct segment_register gdt, tr, prev_tr, segr; struct desc_struct *optss_desc = NULL, *nptss_desc = NULL, tss_desc; bool_t otd_writable, ntd_writable; - unsigned int eflags; + unsigned int eflags, new_cpl; pagefault_info_t pfinfo; int exn_raised, rc; struct tss32 tss; @@ -2918,7 +2917,9 @@ void hvm_task_switch( if ( rc != HVMCOPY_okay ) goto out; - if ( hvm_load_segment_selector(x86_seg_ldtr, tss.ldt, 0) ) + new_cpl = tss.eflags & X86_EFLAGS_VM ? 3 : tss.cs & 3; + + if ( hvm_load_segment_selector(x86_seg_ldtr, tss.ldt, new_cpl, 0) ) goto out; rc = hvm_set_cr3(tss.cr3, 1); @@ -2939,12 +2940,12 @@ void hvm_task_switch( regs->rdi = tss.edi; exn_raised = 0; - if ( hvm_load_segment_selector(x86_seg_es, tss.es, tss.eflags) || - hvm_load_segment_selector(x86_seg_cs, tss.cs, tss.eflags) || - hvm_load_segment_selector(x86_seg_ss, tss.ss, tss.eflags) || - hvm_load_segment_selector(x86_seg_ds, tss.ds, tss.eflags) || - hvm_load_segment_selector(x86_seg_fs, tss.fs, tss.eflags) || - hvm_load_segment_selector(x86_seg_gs, tss.gs, tss.eflags) ) + if ( hvm_load_segment_selector(x86_seg_es, tss.es, new_cpl, tss.eflags) || + hvm_load_segment_selector(x86_seg_cs, tss.cs, new_cpl, tss.eflags) || + hvm_load_segment_selector(x86_seg_ss, tss.ss, new_cpl, tss.eflags) || + hvm_load_segment_selector(x86_seg_ds, tss.ds, new_cpl, tss.eflags) || + hvm_load_segment_selector(x86_seg_fs, tss.fs, new_cpl, tss.eflags) || + hvm_load_segment_selector(x86_seg_gs, tss.gs, new_cpl, tss.eflags) ) exn_raised = 1; if ( taskswitch_reason == TSW_call_or_int ) -- 2.30.2