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| author | Jan Beulich <jbeulich@suse.com> | 2013-04-18 16:23:07 +0200 |
|---|---|---|
| committer | Jan Beulich <jbeulich@suse.com> | 2013-04-18 16:23:07 +0200 |
| commit | 584eb7c15e4c94baaba93468776572dd7373a33c (patch) | |
| tree | f647c43dc022c026c810083d0fbe3d68906f222f | |
| parent | f4537b51116009bfb8359681a758ef5860cfd0db (diff) | |
| download | xen-584eb7c15e4c94baaba93468776572dd7373a33c.tar.gz xen-584eb7c15e4c94baaba93468776572dd7373a33c.tar.bz2 xen-584eb7c15e4c94baaba93468776572dd7373a33c.zip | |
x86: clear EFLAGS.NT in SYSENTER entry path
... as it causes problems if we happen to exit back via IRET: In the
course of trying to handle the fault, the hypervisor creates a stack
frame by hand, and uses PUSHFQ to set the respective EFLAGS field, but
expects to be able to IRET through that stack frame to the second
portion of the fixup code (which causes a #GP due to the stored EFLAGS
having NT set).
And even if this worked (e.g if we cleared NT in that path), it would
then (through the fail safe callback) cause a #GP in the guest with the
SYSENTER handler's first instruction as the source, which in turn would
allow guest user mode code to crash the guest kernel.
Inject a #GP on the fake (NULL) address of the SYSENTER instruction
instead, just like in the case where the guest kernel didn't register
a corresponding entry point.
On 32-bit we also need to make sure we clear SYSENTER_CS for all CPUs
(neither #RESET nor #INIT guarantee this).
This is CVE-2013-1917 / XSA-44.
Reported-by: Andrew Cooper <andrew.cooper3@citirx.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Tested-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
master commit: fdac9515607b757c044e7ef0d61b1453ef999b08
master date: 2013-04-18 16:00:35 +0200
| -rw-r--r-- | xen/arch/x86/acpi/suspend.c | 8 | ||||
| -rw-r--r-- | xen/arch/x86/cpu/common.c | 5 | ||||
| -rw-r--r-- | xen/arch/x86/x86_64/entry.S | 7 |
3 files changed, 17 insertions, 3 deletions
diff --git a/xen/arch/x86/acpi/suspend.c b/xen/arch/x86/acpi/suspend.c index 6f2ff5b82b..1c3aff4115 100644 --- a/xen/arch/x86/acpi/suspend.c +++ b/xen/arch/x86/acpi/suspend.c @@ -81,8 +81,12 @@ void restore_rest_processor_state(void) } #else /* !defined(CONFIG_X86_64) */ - if ( supervisor_mode_kernel && cpu_has_sep ) - wrmsr(MSR_IA32_SYSENTER_ESP, &this_cpu(init_tss).esp1, 0); + if ( cpu_has_sep ) + { + wrmsr(MSR_IA32_SYSENTER_CS, 0, 0); + if ( supervisor_mode_kernel ) + wrmsr(MSR_IA32_SYSENTER_ESP, &this_cpu(init_tss).esp1, 0); + } #endif /* Maybe load the debug registers. */ diff --git a/xen/arch/x86/cpu/common.c b/xen/arch/x86/cpu/common.c index c3ddab69bf..a3a6b96d5e 100644 --- a/xen/arch/x86/cpu/common.c +++ b/xen/arch/x86/cpu/common.c @@ -715,8 +715,11 @@ void __cpuinit cpu_init(void) #if defined(CONFIG_X86_32) t->ss0 = __HYPERVISOR_DS; t->esp0 = get_stack_bottom(); - if ( supervisor_mode_kernel && cpu_has_sep ) + if ( cpu_has_sep ) { + wrmsr(MSR_IA32_SYSENTER_CS, 0, 0); + if ( supervisor_mode_kernel ) wrmsr(MSR_IA32_SYSENTER_ESP, &t->esp1, 0); + } #elif defined(CONFIG_X86_64) /* Bottom-of-stack must be 16-byte aligned! */ BUG_ON((get_stack_bottom() & 15) != 0); diff --git a/xen/arch/x86/x86_64/entry.S b/xen/arch/x86/x86_64/entry.S index 2b8c99a315..7b392d8bde 100644 --- a/xen/arch/x86/x86_64/entry.S +++ b/xen/arch/x86/x86_64/entry.S @@ -288,7 +288,14 @@ sysenter_eflags_saved: movl $3,UREGS_cs(%rsp) /* ring 3 null cs */ movq VCPU_sysenter_addr(%rbx),%rax setne %cl + testl $X86_EFLAGS_NT,UREGS_eflags(%rsp) leaq VCPU_trap_bounce(%rbx),%rdx +UNLIKELY_START(nz, sysenter_nt_set) + pushfq + andl $~X86_EFLAGS_NT,(%rsp) + popfq + xorl %eax,%eax +UNLIKELY_END(sysenter_nt_set) testq %rax,%rax leal (,%rcx,TBF_INTERRUPT),%ecx UNLIKELY_START(z, sysenter_gpf) |