* [2.24 COMMITTED] arm: mark __startcontext as .cantunwind (bug 20435)
@ 2016-01-01 0:00 Florian Weimer
0 siblings, 0 replies; only message in thread
From: Florian Weimer @ 2016-01-01 0:00 UTC (permalink / raw)
To: libc-stable
__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.
2016-08-15 Andreas Schwab <schwab@suse.de>
[BZ #20435]
* sysdeps/unix/sysv/linux/arm/setcontext.S (__startcontext): Mark
as .cantunwind.
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 <http://sourceware.org/bugzilla/>
using `glibc' in the "product" field.
\f
+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)
+
+\f
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
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2016-01-01 0:00 [2.24 COMMITTED] arm: mark __startcontext as .cantunwind (bug 20435) Florian Weimer
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