6.12-stable review patch. If anyone has any objections, please let me know.
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From: Will Deacon will@kernel.org
commit 67ab51cbdfee02ef07fb9d7d14cc0bf6cb5a5e5c upstream.
Commit 18011eac28c7 ("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: 18011eac28c7 ("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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/arm64/kernel/process.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/arch/arm64/kernel/process.c +++ b/arch/arm64/kernel/process.c @@ -442,7 +442,7 @@ static void tls_thread_switch(struct tas
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);