diff options
Diffstat (limited to 'system/xen/patches/xsa170.patch')
| -rw-r--r-- | system/xen/patches/xsa170.patch | 79 |
1 files changed, 79 insertions, 0 deletions
diff --git a/system/xen/patches/xsa170.patch b/system/xen/patches/xsa170.patch new file mode 100644 index 0000000000..f71fa19130 --- /dev/null +++ b/system/xen/patches/xsa170.patch @@ -0,0 +1,79 @@ +x86/VMX: sanitize rIP before re-entering guest + +... to prevent guest user mode arranging for a guest crash (due to +failed VM entry). (On the AMD system I checked, hardware is doing +exactly the canonicalization being added here.) + +Note that fixing this in an architecturally correct way would be quite +a bit more involved: Making the x86 instruction emulator check all +branch targets for validity, plus dealing with invalid rIP resulting +from update_guest_eip() or incoming directly during a VM exit. The only +way to get the latter right would be by not having hardware do the +injection. + +Note further that there are a two early returns from +vmx_vmexit_handler(): One (through vmx_failed_vmentry()) leads to +domain_crash() anyway, and the other covers real mode only and can +neither occur with a non-canonical rIP nor result in an altered rIP, +so we don't need to force those paths through the checking logic. + +This is XSA-170. + +Reported-by: 刘令 <liuling-it@360.cn> +Signed-off-by: Jan Beulich <jbeulich@suse.com> +Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com> +Tested-by: Andrew Cooper <andrew.cooper3@citrix.com> + +--- a/xen/arch/x86/hvm/vmx/vmx.c ++++ b/xen/arch/x86/hvm/vmx/vmx.c +@@ -2968,7 +2968,7 @@ static int vmx_handle_apic_write(void) + void vmx_vmexit_handler(struct cpu_user_regs *regs) + { + unsigned long exit_qualification, exit_reason, idtv_info, intr_info = 0; +- unsigned int vector = 0; ++ unsigned int vector = 0, mode; + struct vcpu *v = current; + + __vmread(GUEST_RIP, ®s->rip); +@@ -3566,6 +3566,41 @@ void vmx_vmexit_handler(struct cpu_user_ + out: + if ( nestedhvm_vcpu_in_guestmode(v) ) + nvmx_idtv_handling(); ++ ++ /* ++ * VM entry will fail (causing the guest to get crashed) if rIP (and ++ * rFLAGS, but we don't have an issue there) doesn't meet certain ++ * criteria. As we must not allow less than fully privileged mode to have ++ * such an effect on the domain, we correct rIP in that case (accepting ++ * this not being architecturally correct behavior, as the injected #GP ++ * fault will then not see the correct [invalid] return address). ++ * And since we know the guest will crash, we crash it right away if it ++ * already is in most privileged mode. ++ */ ++ mode = vmx_guest_x86_mode(v); ++ if ( mode == 8 ? !is_canonical_address(regs->rip) ++ : regs->rip != regs->_eip ) ++ { ++ struct segment_register ss; ++ ++ gprintk(XENLOG_WARNING, "Bad rIP %lx for mode %u\n", regs->rip, mode); ++ ++ vmx_get_segment_register(v, x86_seg_ss, &ss); ++ if ( ss.attr.fields.dpl ) ++ { ++ __vmread(VM_ENTRY_INTR_INFO, &intr_info); ++ if ( !(intr_info & INTR_INFO_VALID_MASK) ) ++ hvm_inject_hw_exception(TRAP_gp_fault, 0); ++ /* Need to fix rIP nevertheless. */ ++ if ( mode == 8 ) ++ regs->rip = (long)(regs->rip << (64 - VADDR_BITS)) >> ++ (64 - VADDR_BITS); ++ else ++ regs->rip = regs->_eip; ++ } ++ else ++ domain_crash(v->domain); ++ } + } + + void vmx_vmenter_helper(const struct cpu_user_regs *regs) |