COSEINC Linux Advisory #2: IA32 System Call Emulation Vulnerability

Linux kernel system calls All Rights Reserved LEGAL DISCLAIMER AS IS AT YOUR OWN RISK local system FOR ANY CONSEQUENTIAL DAMAGES 18th September 24th September Security Researcher Wojciech Purczynski providing code 32-bit vendor Vulnerability Research

===[ 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.

All Rights Reserved.

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USE AT YOUR OWN RISK.