[3.13.y.z extended stable] Patch "sparc64: Do not define thread fpregs save area as zero-length array." has been added to staging queue

Kamal Mostafa kamal at canonical.com
Fri Oct 31 20:53:28 UTC 2014

This is a note to let you know that I have just added a patch titled

    sparc64: Do not define thread fpregs save area as zero-length array.

to the linux-3.13.y-queue branch of the 3.13.y.z extended stable tree 
which can be found at:


This patch is scheduled to be released in version

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y.z tree, see



>From 21113443b34215d14078153532330703102bcbd4 Mon Sep 17 00:00:00 2001
From: "David S. Miller" <davem at davemloft.net>
Date: Sat, 18 Oct 2014 23:12:33 -0400
Subject: sparc64: Do not define thread fpregs save area as zero-length array.

[ Upstream commit e2653143d7d79a49f1a961aeae1d82612838b12c ]

This breaks the stack end corruption detection facility.

What that facility does it write a magic value to "end_of_stack()"
and checking to see if it gets overwritten.

"end_of_stack()" is "task_thread_info(p) + 1", which for sparc64 is
the beginning of the FPU register save area.

So once the user uses the FPU, the magic value is overwritten and the
debug checks trigger.

Fix this by making the size explicit.

Due to the size we use for the fpsaved[], gsr[], and xfsr[] arrays we
are limited to 7 levels of FPU state saves.  So each FPU register set
is 256 bytes, allocate 256 * 7 for the fpregs area.

Reported-by: Meelis Roos <mroos at linux.ee>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
 arch/sparc/include/asm/thread_info_64.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/sparc/include/asm/thread_info_64.h b/arch/sparc/include/asm/thread_info_64.h
index f85dc85..cc6275c 100644
--- a/arch/sparc/include/asm/thread_info_64.h
+++ b/arch/sparc/include/asm/thread_info_64.h
@@ -63,7 +63,8 @@ struct thread_info {
 	struct pt_regs		*kern_una_regs;
 	unsigned int		kern_una_insn;

-	unsigned long		fpregs[0] __attribute__ ((aligned(64)));
+	unsigned long		fpregs[(7 * 256) / sizeof(unsigned long)]
+		__attribute__ ((aligned(64)));

 #endif /* !(__ASSEMBLY__) */

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