[UNIX] IA32 System Call Emulation Vulnerability

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IA32 System Call Emulation Vulnerability
------------------------------------------------------------------------

SUMMARY

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

DETAILS

Vulnerable Systems:
* Linux 2.6
* Linux 2.4

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

ADDITIONAL INFORMATION

The information has been provided by <mailto:cliph@research.coseinc.com>
Wojciech Purczynski.

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