Patch "arm64: flush FP/SIMD state correctly after execve()" has been added to the 3.18-stable tree

This is a note to let you know that I've just added the patch titled

arm64: flush FP/SIMD state correctly after execve()

to the 3.18-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
arm64-flush-fp-simd-state-correctly-after-execve.patch
and it can be found in the queue-3.18 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Ard Biesheuvel <[email protected]>
Date: Thu, 27 Aug 2015 07:12:33 +0100
Subject: arm64: flush FP/SIMD state correctly after execve()

From: Ard Biesheuvel <[email protected]>

commit 674c242c9323d3c293fc4f9a3a3a619fe3063290 upstream.

When a task calls execve(), its FP/SIMD state is flushed so that none of the original program state is observeable by the incoming program.

However, since this flushing consists of setting the in-memory copy of the FP/SIMD state to all zeroes, the CPU field is set to CPU 0 as well, which indicates to the lazy FP/SIMD preserve/restore code that the FP/SIMD state does not need to be reread from memory if the task is scheduled again on CPU 0 without any other tasks having entered userland (or used the FP/SIMD in kernel mode) on the same CPU in the mean time. If this happens, the FP/SIMD state of the old program will still be present in the registers when the new program starts.

So set the CPU field to the invalid value of NR_CPUS when performing the flush, by calling fpsimd_flush_task_state().

---
 arch/arm64/kernel/fpsimd.c |    1 +
 1 file changed, 1 insertion(+)

@@ -157,6 +157,7 @@ void fpsimd_thread_switch(struct task_st
 void fpsimd_flush_thread(void)
 {
 	memset(&current->thread.fpsimd_state, 0, sizeof(struct fpsimd_state));
+	fpsimd_flush_task_state(current);
 	set_thread_flag(TIF_FOREIGN_FPSTATE);
 }
 

Patches currently in stable-queue which might be from [email protected] are

queue-3.18/arm64-flush-fp-simd-state-correctly-after-execve.patch queue-3.18/arm64-fpsimd-prevent-registers-leaking-across-exec.patch