[PATCH 4.2 029/134] arm64: flush FP/SIMD state correctly after execve()

From: Greg Kroah-Hartman
Date: Sat Sep 26 2015 - 18:20:00 EST

4.2-stable review patch. If anyone has any objections, please let me know.


From: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>

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

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().

Reported-by: Chunyan Zhang <chunyan.zhang@xxxxxxxxxxxxxx>
Reported-by: Janet Liu <janet.liu@xxxxxxxxxxxxxx>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

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

--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -158,6 +158,7 @@ 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);

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