Date: Wed, 9 Jul 2014 10:38:13 +0400 From: Solar Designer <solar@...nwall.com> To: oss-security@...ts.openwall.com Subject: Re: CVE-2014-4699: Linux ptrace bug On Tue, Jul 08, 2014 at 03:15:47PM -0700, Andy Lutomirski wrote: > In the event that anyone changes TASK_SIZE_MAX to equal the first > non-canonical address, then this is the least of your worries: someone > can put a syscall instruction at the very last canonical address, and > game over. You're right. > This bug affected a lot of operating systems a few years ago, but AFAIK > Linux was never vulnerable. Looks like it was until 22.214.171.124: http://lwn.net/Articles/137821/ Andi Kleen: [...] o x86_64: Add a guard page at the end of the 47bit address space o x86_64: Fix canonical checking for segment registers in ptrace o x86_64: check if ptrace RIP is canonical http://www.x86-64.org/pipermail/discuss/2005-May/006031.html https://kernel.googlesource.com/pub/scm/linux/kernel/git/stable/stable-queue/+/9cb395089b0a1aeaabd7900437c146a45a7ff067/126.96.36.199/x86_64-add-guard-page.patch "Add a guard page at the end of the 47bit address space. This works around a bug in the AMD K8 CPUs." https://access.redhat.com/security/cve/CVE-2005-1762 "The ptrace call in the Linux kernel 188.8.131.52 and 2.6.10 for the AMD64 platform allows local users to cause a denial of service (kernel crash) via a "non-canonical" address." So apparently the ptrace attack vector was tracked as CVE-2005-1762 at the time, whereas TASK_SIZE being equal to the first non-canonical address and triggering "a bug in the AMD K8 CPUs" (the known impact at the time, whatever it was) wasn't tracked as a security issue. Also related: "Bug 437712 - ptrace: PTRACE_SETREGS does not set RIP" https://bugzilla.redhat.com/show_bug.cgi?id=437712 (some discussion of an earlier fix at ptrace level, NOTABUG by that time). Alexander
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