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arm64: tls: Fix context-switching of tpidrro_el0 when kpti is enabled

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Commit 18011eac28 ("arm64: tls: Avoid unconditional zeroing of
tpidrro_el0 for native tasks") tried to optimise the context switching
of tpidrro_el0 by eliding the clearing of the register when switching
to a native task with kpti enabled, on the erroneous assumption that
the kpti trampoline entry code would already have taken care of the
write.

Although the kpti trampoline does zero the register on entry from a
native task, the check in tls_thread_switch() is on the *next* task and
so we can end up leaving a stale, non-zero value in the register if the
previous task was 32-bit.

Drop the broken optimisation and zero tpidrro_el0 unconditionally when
switching to a native 64-bit task.

Cc: Mark Rutland <mark.rutland@arm.com>
Cc: stable@vger.kernel.org
Fixes: 18011eac28 ("arm64: tls: Avoid unconditional zeroing of tpidrro_el0 for native tasks")
Signed-off-by: Will Deacon <will@kernel.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Link: https://lore.kernel.org/r/20241114095332.23391-1-will@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Will Deacon 2024-11-14 09:53:32 +00:00 committed by Catalin Marinas
parent c0139f6cbb
commit 67ab51cbdf
1 changed files with 1 additions and 1 deletions
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2
arch/arm64/kernel/process.c
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@ -439,7 +439,7 @@ static void tls_thread_switch(struct task_struct *next)
if (is_compat_thread(task_thread_info(next)))
write_sysreg(next->thread.uw.tp_value, tpidrro_el0);
else if (!arm64_kernel_unmapped_at_el0())
else
write_sysreg(0, tpidrro_el0);
write_sysreg(*task_user_tls(next), tpidr_el0);