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Subject[PATCH 4.9 26/66] arm64: Move BP hardening to check_and_switch_context
Date
4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Mark Rutland <mark.rutland@arm.com>


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]
Tested-by: Greg Hackmann <ghackmann@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/arm64/mm/context.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

--- a/arch/arm64/mm/context.c
+++ b/arch/arm64/mm/context.c
@@ -230,6 +230,9 @@ void check_and_switch_context(struct mm_
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_workaro
"ic iallu; dsb nsh; isb",
ARM64_WORKAROUND_CAVIUM_27456,
CONFIG_CAVIUM_ERRATUM_27456));
-
- arm64_apply_bp_hardening();
}

static int asids_init(void)

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