arm64: flush FP/SIMD state correctly after execve()
authorArd Biesheuvel <ard.biesheuvel@linaro.org>
Thu, 27 Aug 2015 06:12:33 +0000 (07:12 +0100)
committerWill Deacon <will.deacon@arm.com>
Thu, 27 Aug 2015 08:55:26 +0000 (09:55 +0100)
commit674c242c9323d3c293fc4f9a3a3a619fe3063290
treed57a5528cbc4c6362ba74bec58ce7d7f88ffbb81
parent5166c20ef95be89d10ffe0140e74df5cf26e9786
arm64: flush FP/SIMD state correctly after execve()

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().

Cc: <stable@vger.kernel.org>
Reported-by: Chunyan Zhang <chunyan.zhang@spreadtrum.com>
Reported-by: Janet Liu <janet.liu@spreadtrum.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
arch/arm64/kernel/fpsimd.c