===[ ABSTRACT ]=========================================================

Insufficient validation of general-purpose register in IA32 system call
emulation code may lead to local system compromise on x86_64 platform.


===[ AFFECTED SOFTWARE ]================================================

Linux 2.6
Linux 2.4

For the exact kernel version please refer to an information provided by
your vendor.


===[ DESCRIPTION ]======================================================

On x86_64 platform the Linux kernel supports compatibility emulation for
IA32 userland applications providing 32-bit system calls amongst other
32-bit resources.

As a result of arch/x86_64/ia32/ia32entry.S code optimization invalid
opcodes was used in the low level assembler routines providing
insufficient validation of %RAX register in the following part of code 
(2.6):

---8<---
sysenter_do_call:
        cmpl    $(IA32_NR_syscalls-1),%eax
        ja      ia32_badsys
        IA32_ARG_FIXUP 1
        call    *ia32_sys_call_table(,%rax,8)
---8<---
cstar_do_call:
        cmpl $IA32_NR_syscalls-1,%eax
        ja  ia32_badsys
        IA32_ARG_FIXUP 1
        call *ia32_sys_call_table(,%rax,8)
---8<---
ia32_do_syscall:
        cmpl $(IA32_NR_syscalls-1),%eax
        ja  ia32_badsys
        IA32_ARG_FIXUP
        call *ia32_sys_call_table(,%rax,8) # xxx: rip relative
---8<---

Improperly validated 64-bit values stored in the %RAX register may lead
to out-of-bounds system call table access resulting in the ability to
execute arbitrary code in the context of the Linux kernel.


===[ IMPACT ]===========================================================

Unprivileged local user may execute arbitrary code in the context of the
Linux kernel running on x86_64 platform.


===[ DISCLOSURE TIMELINE ]==============================================

18th September 2007	Vendor notification
24th September 2007	Public disclosure


===[ AUTHOR ]===========================================================

Wojciech Purczynski <cliph@research.coseinc.com>

Wojciech Purczynski is a Security Researcher at Vulnerability Research
Labs, COSEINC PTE Ltd. Wojciech Purczynski is also a member of iSEC
Security Research.


===[ LEGAL DISCLAIMER ]=================================================

Copyright (c) 2007 Wojciech Purczynski
Copyright (c) 2007 COSEINC PTE Ltd.

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