From: Marc Zyngier marc.zyngier@arm.com
commit a8e4c0a919ae310944ed2c9ace11cf3ccd8a609b upstream.
We call arm64_apply_bp_hardening() from post_ttbr_update_workaround, which has the unexpected consequence of being triggered on every exception return to userspace when ARM64_SW_TTBR0_PAN is selected, even if no context switch actually occured.
This is a bit suboptimal, and it would be more logical to only invalidate the branch predictor when we actually switch to a different mm.
In order to solve this, move the call to arm64_apply_bp_hardening() into check_and_switch_context(), where we're guaranteed to pick a different mm context.
Acked-by: Will Deacon will.deacon@arm.com Signed-off-by: Marc Zyngier marc.zyngier@arm.com Signed-off-by: Catalin Marinas catalin.marinas@arm.com Signed-off-by: Mark Rutland mark.rutland@arm.com [v4.9 backport] --- arch/arm64/mm/context.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/arch/arm64/mm/context.c b/arch/arm64/mm/context.c index accf7ead3945..62d976e843fc 100644 --- a/arch/arm64/mm/context.c +++ b/arch/arm64/mm/context.c @@ -230,6 +230,9 @@ void check_and_switch_context(struct mm_struct *mm, unsigned int cpu) raw_spin_unlock_irqrestore(&cpu_asid_lock, flags);
switch_mm_fastpath: + + arm64_apply_bp_hardening(); + cpu_switch_mm(mm->pgd, mm); }
@@ -240,8 +243,6 @@ asmlinkage void post_ttbr_update_workaround(void) "ic iallu; dsb nsh; isb", ARM64_WORKAROUND_CAVIUM_27456, CONFIG_CAVIUM_ERRATUM_27456)); - - arm64_apply_bp_hardening(); }
static int asids_init(void)