linux-kernel - [PATCH 3.16.y-ckt 060/133] arm64: flush FP/SIMD state correctly after execve()

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Message-Id: <1443606681-7124-61-git-send-email-luis.henriques@canonical.com>
Date:	Wed, 30 Sep 2015 10:50:08 +0100
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Will Deacon <will.deacon@....com>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 060/133] arm64: flush FP/SIMD state correctly after execve()

3.16.7-ckt18 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ard Biesheuvel <ard.biesheuvel@...aro.org>

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().

Reported-by: Chunyan Zhang <chunyan.zhang@...eadtrum.com>
Reported-by: Janet Liu <janet.liu@...eadtrum.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Signed-off-by: Will Deacon <will.deacon@....com>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 arch/arm64/kernel/fpsimd.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index ad8aebb1cdef..a43a40b6a846 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -157,6 +157,7 @@ void fpsimd_thread_switch(struct task_struct *next)
 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);
 }

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