79 lines
3.1 KiB
Diff
79 lines
3.1 KiB
Diff
x86/VMX: sanitize rIP before re-entering guest
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... to prevent guest user mode arranging for a guest crash (due to
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failed VM entry). (On the AMD system I checked, hardware is doing
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exactly the canonicalization being added here.)
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Note that fixing this in an architecturally correct way would be quite
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a bit more involved: Making the x86 instruction emulator check all
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branch targets for validity, plus dealing with invalid rIP resulting
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from update_guest_eip() or incoming directly during a VM exit. The only
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way to get the latter right would be by not having hardware do the
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injection.
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Note further that there are a two early returns from
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vmx_vmexit_handler(): One (through vmx_failed_vmentry()) leads to
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domain_crash() anyway, and the other covers real mode only and can
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neither occur with a non-canonical rIP nor result in an altered rIP,
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so we don't need to force those paths through the checking logic.
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This is XSA-170.
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Reported-by: 刘令 <liuling-it@360.cn>
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Signed-off-by: Jan Beulich <jbeulich@suse.com>
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Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
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Tested-by: Andrew Cooper <andrew.cooper3@citrix.com>
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--- a/xen/arch/x86/hvm/vmx/vmx.c
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+++ b/xen/arch/x86/hvm/vmx/vmx.c
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@@ -2968,7 +2968,7 @@ static int vmx_handle_apic_write(void)
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void vmx_vmexit_handler(struct cpu_user_regs *regs)
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{
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unsigned long exit_qualification, exit_reason, idtv_info, intr_info = 0;
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- unsigned int vector = 0;
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+ unsigned int vector = 0, mode;
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struct vcpu *v = current;
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__vmread(GUEST_RIP, ®s->rip);
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@@ -3566,6 +3566,41 @@ void vmx_vmexit_handler(struct cpu_user_
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out:
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if ( nestedhvm_vcpu_in_guestmode(v) )
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nvmx_idtv_handling();
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+
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+ /*
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+ * VM entry will fail (causing the guest to get crashed) if rIP (and
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+ * rFLAGS, but we don't have an issue there) doesn't meet certain
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+ * criteria. As we must not allow less than fully privileged mode to have
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+ * such an effect on the domain, we correct rIP in that case (accepting
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+ * this not being architecturally correct behavior, as the injected #GP
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+ * fault will then not see the correct [invalid] return address).
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+ * And since we know the guest will crash, we crash it right away if it
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+ * already is in most privileged mode.
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+ */
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+ mode = vmx_guest_x86_mode(v);
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+ if ( mode == 8 ? !is_canonical_address(regs->rip)
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+ : regs->rip != regs->_eip )
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+ {
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+ struct segment_register ss;
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+
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+ gprintk(XENLOG_WARNING, "Bad rIP %lx for mode %u\n", regs->rip, mode);
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+
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+ vmx_get_segment_register(v, x86_seg_ss, &ss);
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+ if ( ss.attr.fields.dpl )
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+ {
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+ __vmread(VM_ENTRY_INTR_INFO, &intr_info);
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+ if ( !(intr_info & INTR_INFO_VALID_MASK) )
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+ hvm_inject_hw_exception(TRAP_gp_fault, 0);
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+ /* Need to fix rIP nevertheless. */
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+ if ( mode == 8 )
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+ regs->rip = (long)(regs->rip << (64 - VADDR_BITS)) >>
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+ (64 - VADDR_BITS);
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+ else
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+ regs->rip = regs->_eip;
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+ }
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+ else
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+ domain_crash(v->domain);
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+ }
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}
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void vmx_vmenter_helper(const struct cpu_user_regs *regs)
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