commit 52f73c383b2418f2d31b798e765ae7d596c35021 upstream
We detect the absence of FP/SIMD after an incapable CPU is brought up, and by then we have kernel threads running already with TIF_FOREIGN_FPSTATE set which could be set for early userspace applications (e.g, modprobe triggered from initramfs) and init. This could cause the applications to loop forever in do_nofity_resume() as we never clear the TIF flag, once we now know that we don't support FP.
Fix this by making sure that we clear the TIF_FOREIGN_FPSTATE flag for tasks which may have them set, as we would have done in the normal case, but avoiding touching the hardware state (since we don't support any).
Cc: stable@vger.kernel.org # v4.14 Cc: Will Deacon will@kernel.org Cc: Mark Rutland mark.rutland@arm.com Reviewed-by: Ard Biesheuvel ardb@kernel.org Reviewed-by: Catalin Marinas catalin.marinas@arm.com Acked-by: Marc Zyngier maz@kernel.org Signed-off-by: Suzuki K Poulose suzuki.poulose@arm.com --- arch/arm64/kernel/fpsimd.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-)
diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c index f4fdf6420ac5..4cd962f6c430 100644 --- a/arch/arm64/kernel/fpsimd.c +++ b/arch/arm64/kernel/fpsimd.c @@ -206,8 +206,19 @@ void fpsimd_preserve_current_state(void) */ void fpsimd_restore_current_state(void) { - if (!system_supports_fpsimd()) + /* + * For the tasks that were created before we detected the absence of + * FP/SIMD, the TIF_FOREIGN_FPSTATE could be set via fpsimd_thread_switch(), + * e.g, init. This could be then inherited by the children processes. + * If we later detect that the system doesn't support FP/SIMD, + * we must clear the flag for all the tasks to indicate that the + * FPSTATE is clean (as we can't have one) to avoid looping for ever in + * do_notify_resume(). + */ + if (!system_supports_fpsimd()) { + clear_thread_flag(TIF_FOREIGN_FPSTATE); return; + }
local_bh_disable();
@@ -229,7 +240,7 @@ void fpsimd_restore_current_state(void) */ void fpsimd_update_current_state(struct fpsimd_state *state) { - if (!system_supports_fpsimd()) + if (WARN_ON(!system_supports_fpsimd())) return;
local_bh_disable();