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glibc-2.24: Fix CVE-2016-6323
[No upstream tracking] -- https://sourceware.org/bugzilla/show_bug.cgi?id=20435
arm: mark __startcontext as .cantunwind, GNU
Glibc bug where the makecontext function would create
an execution context which is incompatible with the unwinder,
causing it to hang when the generation of a backtrace is attempted.
Upstream-Status: Backport [https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=9e2ff6c9cc54c0b4402b8d49e4abe7000fde7617]
CVE: CVE-2016-6323
Signed-off-by: Andrej Valek <andrej.valek@siemens.com>
Signed-off-by: Pascal Bach <pascal.bach@siemens.com>
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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