| From | Greg Kroah-Hartman <> | Subject | [PATCH 4.14 038/195] [Variant 3/Meltdown] arm64: tls: Avoid unconditional zeroing of tpidrro_el0 for native tasks | Date | Thu, 15 Feb 2018 16:15:29 +0100 |
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4.14-stable review patch. If anyone has any objections, please let me know.
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From: Will Deacon <will.deacon@arm.com>
Commit 18011eac28c7 upstream.
When unmapping the kernel at EL0, we use tpidrro_el0 as a scratch register during exception entry from native tasks and subsequently zero it in the kernel_ventry macro. We can therefore avoid zeroing tpidrro_el0 in the context-switch path for native tasks using the entry trampoline.
Reviewed-by: Mark Rutland <mark.rutland@arm.com> Tested-by: Laura Abbott <labbott@redhat.com> Tested-by: Shanker Donthineni <shankerd@codeaurora.org> Signed-off-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> --- arch/arm64/kernel/process.c | 12 +++++------- 1 file changed, 5 insertions(+), 7 deletions(-)
--- a/arch/arm64/kernel/process.c +++ b/arch/arm64/kernel/process.c @@ -314,16 +314,14 @@ void tls_preserve_current_state(void) static void tls_thread_switch(struct task_struct *next) { - unsigned long tpidr, tpidrro; - tls_preserve_current_state(); - tpidr = *task_user_tls(next); - tpidrro = is_compat_thread(task_thread_info(next)) ? - next->thread.tp_value : 0; + if (is_compat_thread(task_thread_info(next))) + write_sysreg(next->thread.tp_value, tpidrro_el0); + else if (!arm64_kernel_unmapped_at_el0()) + write_sysreg(0, tpidrro_el0); - write_sysreg(tpidr, tpidr_el0); - write_sysreg(tpidrro, tpidrro_el0); + write_sysreg(*task_user_tls(next), tpidr_el0); } /* Restore the UAO state depending on next's addr_limit */
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