Jan Beulich
2009-May-13 14:21 UTC
[Xen-devel] [PATCH] linux/i386: hypervisor_callback adjustments
The missing check of the interrupted code''s code selector in hypervisor_callback() allowed a user mode application to oops (and perhaps crash) the kernel. Further adjustments: - the ''main'' critical region does not include the jmp following the disabling of interrupts - the sysexit_[se]crit range checks got broken at some point - the sysexit ciritcal region is always at higher addresses than the ''main'' one, yielding the check pointless (but consuming execution time); since the supervisor mode kernel isn''t actively used afaict, I moved that code into an #ifdef using a hypothetical config option - the use of a numeric label across more than 300 lines of code always seemed pretty fragile to me, so the patch replaces this with a local named label - streamlined the critical_region_fixup code to eliminate a branch As usual, written and tested on 2.6.30-rc4 and made apply to the 2.6.18 tree without further testing. Signed-off-by: Jan Beulich <jbeulich@novell.com> --- head-2009-05-04.orig/arch/i386/kernel/entry-xen.S 2009-05-13 14:06:24.000000000 +0200 +++ head-2009-05-04/arch/i386/kernel/entry-xen.S 2009-05-13 14:11:53.000000000 +0200 @@ -529,8 +531,8 @@ scrit: /**** START OF CRITICAL REGION ** .previous 14: __DISABLE_INTERRUPTS TRACE_IRQS_OFF - jmp 11f ecrit: /**** END OF CRITICAL REGION ****/ + jmp .Ldo_upcall CFI_RESTORE_STATE hypervisor_iret: @@ -788,17 +790,23 @@ ENTRY(hypervisor_callback) pushl %eax CFI_ADJUST_CFA_OFFSET 4 SAVE_ALL + testb $2,CS(%esp) movl EIP(%esp),%eax + jnz .Ldo_upcall cmpl $scrit,%eax - jb 11f + jb 0f cmpl $ecrit,%eax jb critical_region_fixup +0: +#ifdef CONFIG_XEN_SUPERVISOR_MODE_KERNEL cmpl $sysexit_scrit,%eax - jb 11f + jb .Ldo_upcall cmpl $sysexit_ecrit,%eax - ja 11f + ja .Ldo_upcall addl $OLDESP,%esp # Remove eflags...ebx from stack frame. -11: push %esp +#endif +.Ldo_upcall: + push %esp CFI_ADJUST_CFA_OFFSET 4 call evtchn_do_upcall add $4,%esp @@ -814,39 +822,35 @@ ENTRY(hypervisor_callback) # provides the number of bytes which have already been popped from the # interrupted stack frame. critical_region_fixup: - movzbl critical_fixup_table-scrit(%eax),%ecx # %eax contains num bytes popped - cmpb $0xff,%cl # 0xff => vcpu_info critical region - jne 15f - xorl %ecx,%ecx -15: leal (%esp,%ecx),%esi # %esi points at end of src region + movsbl critical_fixup_table-scrit(%eax),%ecx # %ecx contains num slots popped + testl %ecx,%ecx + leal (%esp,%ecx,4),%esi # %esi points at end of src region leal OLDESP(%esp),%edi # %edi points at end of dst region - shrl $2,%ecx # convert words to bytes - je 17f # skip loop if nothing to copy + jle 17f # skip loop if nothing to copy 16: subl $4,%esi # pre-decrementing copy loop subl $4,%edi movl (%esi),%eax movl %eax,(%edi) loop 16b 17: movl %edi,%esp # final %edi is top of merged stack - jmp 11b + jmp .Ldo_upcall .section .rodata,"a" critical_fixup_table: - .byte 0xff,0xff,0xff # testb $0xff,(%esi) = __TEST_PENDING - .byte 0xff,0xff # jnz 14f - .byte 0x00 # pop %ebx - .byte 0x04 # pop %ecx - .byte 0x08 # pop %edx - .byte 0x0c # pop %esi - .byte 0x10 # pop %edi - .byte 0x14 # pop %ebp - .byte 0x18 # pop %eax - .byte 0x1c # pop %ds - .byte 0x20 # pop %es - .byte 0x24,0x24,0x24 # add $4,%esp - .byte 0x28 # iret - .byte 0xff,0xff,0xff,0xff # movb $1,1(%esi) - .byte 0x00,0x00 # jmp 11b + .byte -1,-1,-1 # testb $0xff,(%esi) = __TEST_PENDING + .byte -1,-1 # jnz 14f + .byte 0 # pop %ebx + .byte 1 # pop %ecx + .byte 2 # pop %edx + .byte 3 # pop %esi + .byte 4 # pop %edi + .byte 5 # pop %ebp + .byte 6 # pop %eax + .byte 7 # pop %ds + .byte 8 # pop %es + .byte 9,9,9 # add $4,%esp + .byte 10 # iret + .byte -1,-1,-1,-1 # movb $1,1(%esi) = __DISABLE_INTERRUPTS .previous # Hypervisor uses this for application faults while it executes. _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel