[v4.9.y,18/42] arm64: Move BP hardening to check_and_switch_context

Message ID 20180412111138.40990-19-mark.rutland@arm.com
State New
Headers show
  • arm64 spectre patches
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Commit Message

Mark Rutland April 12, 2018, 11:11 a.m.
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);
+	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_apply_bp_hardening();
 static int asids_init(void)