From 72450627ba8a173366265af550115de951f148c9 Mon Sep 17 00:00:00 2001 From: Andreas Schwab Date: Thu, 18 Aug 2016 11:38:28 +0200 Subject: [PATCH 09] arm: mark __startcontext as .cantunwind (bug 20435) __startcontext marks the bottom of the call stack of the contexts created by makecontext. (cherry picked from commit 9e2ff6c9cc54c0b4402b8d49e4abe7000fde7617) Also includes the NEWS update, cherry-picked from commits 056dd72af83f5459ce6d545a49dea6dba7d635dc and 4d047efdbc55b0d68947cde682e5363d16a66294. --- ChangeLog | 6 ++++++ NEWS | 11 +++++++++++ sysdeps/unix/sysv/linux/arm/setcontext.S | 7 +++++++ 3 files changed, 24 insertions(+) diff --git a/ChangeLog b/ChangeLog index 9dfd24d..734e34b 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,9 @@ +2016-08-15 Andreas Schwab + + [BZ #20435] + * sysdeps/unix/sysv/linux/arm/setcontext.S (__startcontext): Mark + as .cantunwind. + 2016-08-17 Florian Weimer [BZ #20452] diff --git a/NEWS b/NEWS index b0447e7..4a042db 100644 --- a/NEWS +++ b/NEWS @@ -5,6 +5,17 @@ See the end for copying conditions. Please send GNU C library bug reports via using `glibc' in the "product" field. +Version 2.24.1 + +Security related changes: + +* On ARM EABI (32-bit), generating a backtrace for execution contexts which + have been created with makecontext could fail to terminate due to a + missing .cantunwind annotation. This has been observed to lead to a hang + (denial of service) in some Go applications compiled with gccgo. Reported + by Andreas Schwab. (CVE-2016-6323) + + Version 2.24 * The minimum Linux kernel version that this version of the GNU C Library diff --git a/sysdeps/unix/sysv/linux/arm/setcontext.S b/sysdeps/unix/sysv/linux/arm/setcontext.S index 603e508..d1f168f 100644 --- a/sysdeps/unix/sysv/linux/arm/setcontext.S +++ b/sysdeps/unix/sysv/linux/arm/setcontext.S @@ -86,12 +86,19 @@ weak_alias(__setcontext, setcontext) /* Called when a makecontext() context returns. Start the context in R4 or fall through to exit(). */ + /* Unwind descriptors are looked up based on PC - 2, so we have to + make sure to mark the instruction preceding the __startcontext + label as .cantunwind. */ + .fnstart + .cantunwind + nop ENTRY(__startcontext) movs r0, r4 bne PLTJMP(__setcontext) @ New context was 0 - exit b PLTJMP(HIDDEN_JUMPTARGET(exit)) + .fnend END(__startcontext) #ifdef PIC -- 2.7.4.GIT