# HG changeset patch # User Jan Beulich # Date 1339497971 -3600 # Node ID 0fec1afa463808d91defa43f12cb744d3258a868 # Parent f08e61b9b33f553b21870d58e7c4f95f2c9ac513 x86-64: fix #GP generation in assembly code When guest use of sysenter (64-bit PV guest) or syscall (32-bit PV guest) gets converted into a GP fault (due to no callback having got registered), we must - honor the GP fault handler's request the keep enabled or mask event delivery - not allow TBF_EXCEPTION to remain set past the generation of the (guest) exception in the vCPU's trap_bounce.flags, as that would otherwise allow for the next exception occurring in guest mode, should it happen to get handled in Xen itself, to nevertheless get bounced to the guest kernel. Also, just like compat mode syscall handling already did, native mode sysenter handling should, when converting to #GP, subtract 2 from the RIP present in the frame so that the guest's GP fault handler would see the fault pointing to the offending instruction instead of past it. Finally, since those exception generating code blocks needed to be modified anyway, convert them to make use of UNLIKELY_{START,END}(). [ This bug is security vulnerability, XSA-8 / CVE-2012-0218. ] Signed-off-by: Jan Beulich Acked-by: Keir Fraser Committed-by: Jan Beulich xen-unstable changeset: 25200:80f4113be500 25204:569d6f05e1ef Committed-by: Ian Jackson diff -r f08e61b9b33f -r 0fec1afa4638 xen/arch/x86/x86_64/asm-offsets.c --- a/xen/arch/x86/x86_64/asm-offsets.c Tue Jun 12 11:38:30 2012 +0100 +++ b/xen/arch/x86/x86_64/asm-offsets.c Tue Jun 12 11:46:11 2012 +0100 @@ -90,6 +90,8 @@ void __dummy__(void) arch.guest_context.trap_ctxt[TRAP_gp_fault].address); OFFSET(VCPU_gp_fault_sel, struct vcpu, arch.guest_context.trap_ctxt[TRAP_gp_fault].cs); + OFFSET(VCPU_gp_fault_flags, struct vcpu, + arch.guest_context.trap_ctxt[TRAP_gp_fault].flags); OFFSET(VCPU_kernel_sp, struct vcpu, arch.guest_context.kernel_sp); OFFSET(VCPU_kernel_ss, struct vcpu, arch.guest_context.kernel_ss); OFFSET(VCPU_guest_context_flags, struct vcpu, arch.guest_context.flags); diff -r f08e61b9b33f -r 0fec1afa4638 xen/arch/x86/x86_64/compat/entry.S --- a/xen/arch/x86/x86_64/compat/entry.S Tue Jun 12 11:38:30 2012 +0100 +++ b/xen/arch/x86/x86_64/compat/entry.S Tue Jun 12 11:46:11 2012 +0100 @@ -214,6 +214,7 @@ 1: call compat_create_bounce_frame ENTRY(compat_post_handle_exception) testb $TBF_EXCEPTION,TRAPBOUNCE_flags(%rdx) jz compat_test_all_events +.Lcompat_bounce_exception: call compat_create_bounce_frame movb $0,TRAPBOUNCE_flags(%rdx) jmp compat_test_all_events @@ -226,19 +227,20 @@ ENTRY(compat_syscall) leaq VCPU_trap_bounce(%rbx),%rdx testl $~3,%esi leal (,%rcx,TBF_INTERRUPT),%ecx - jz 2f -1: movq %rax,TRAPBOUNCE_eip(%rdx) +UNLIKELY_START(z, compat_syscall_gpf) + movl $TRAP_gp_fault,UREGS_entry_vector(%rsp) + subl $2,UREGS_rip(%rsp) + movl $0,TRAPBOUNCE_error_code(%rdx) + movl VCPU_gp_fault_addr(%rbx),%eax + movzwl VCPU_gp_fault_sel(%rbx),%esi + testb $4,VCPU_gp_fault_flags(%rbx) + setnz %cl + leal TBF_EXCEPTION|TBF_EXCEPTION_ERRCODE(,%rcx,TBF_INTERRUPT),%ecx +UNLIKELY_END(compat_syscall_gpf) + movq %rax,TRAPBOUNCE_eip(%rdx) movw %si,TRAPBOUNCE_cs(%rdx) movb %cl,TRAPBOUNCE_flags(%rdx) - call compat_create_bounce_frame - jmp compat_test_all_events -2: movl $TRAP_gp_fault,UREGS_entry_vector(%rsp) - subl $2,UREGS_rip(%rsp) - movq VCPU_gp_fault_addr(%rbx),%rax - movzwl VCPU_gp_fault_sel(%rbx),%esi - movb $(TBF_EXCEPTION|TBF_EXCEPTION_ERRCODE|TBF_INTERRUPT),%cl - movl $0,TRAPBOUNCE_error_code(%rdx) - jmp 1b + jmp .Lcompat_bounce_exception ENTRY(compat_sysenter) cmpl $TRAP_gp_fault,UREGS_entry_vector(%rsp) diff -r f08e61b9b33f -r 0fec1afa4638 xen/arch/x86/x86_64/entry.S --- a/xen/arch/x86/x86_64/entry.S Tue Jun 12 11:38:30 2012 +0100 +++ b/xen/arch/x86/x86_64/entry.S Tue Jun 12 11:46:11 2012 +0100 @@ -289,19 +289,21 @@ sysenter_eflags_saved: leaq VCPU_trap_bounce(%rbx),%rdx testq %rax,%rax leal (,%rcx,TBF_INTERRUPT),%ecx - jz 2f -1: movq VCPU_domain(%rbx),%rdi +UNLIKELY_START(z, sysenter_gpf) + movl $TRAP_gp_fault,UREGS_entry_vector(%rsp) + subq $2,UREGS_rip(%rsp) + movl %eax,TRAPBOUNCE_error_code(%rdx) + movq VCPU_gp_fault_addr(%rbx),%rax + testb $4,VCPU_gp_fault_flags(%rbx) + setnz %cl + leal TBF_EXCEPTION|TBF_EXCEPTION_ERRCODE(,%rcx,TBF_INTERRUPT),%ecx +UNLIKELY_END(sysenter_gpf) + movq VCPU_domain(%rbx),%rdi movq %rax,TRAPBOUNCE_eip(%rdx) movb %cl,TRAPBOUNCE_flags(%rdx) testb $1,DOMAIN_is_32bit_pv(%rdi) jnz compat_sysenter - call create_bounce_frame - jmp test_all_events -2: movl %eax,TRAPBOUNCE_error_code(%rdx) - movq VCPU_gp_fault_addr(%rbx),%rax - movb $(TBF_EXCEPTION|TBF_EXCEPTION_ERRCODE|TBF_INTERRUPT),%cl - movl $TRAP_gp_fault,UREGS_entry_vector(%rsp) - jmp 1b + jmp .Lbounce_exception ENTRY(int80_direct_trap) pushq $0 @@ -493,6 +495,7 @@ 1: movq %rsp,%rdi jnz compat_post_handle_exception testb $TBF_EXCEPTION,TRAPBOUNCE_flags(%rdx) jz test_all_events +.Lbounce_exception: call create_bounce_frame movb $0,TRAPBOUNCE_flags(%rdx) jmp test_all_events