arm64: entry-common: don't touch daif before bp-hardening

The previous patches mechanically transformed the assembly version of
entry.S to entry-common.c for synchronous exceptions.

The C version of local_daif_restore() doesn't quite do the same thing
as the assembly versions if pseudo-NMI is in use. In particular,
| local_daif_restore(DAIF_PROCCTX_NOIRQ)
will still allow pNMI to be delivered. This is not the behaviour
do_el0_ia_bp_hardening() and do_sp_pc_abort() want as it should not
be possible for the PMU handler to run as an NMI until the bp-hardening
sequence has run.

The bp-hardening calls were placed where they are because this was the
first C code to run after the relevant exceptions. As we've now moved
that point earlier, move the checks and calls earlier too.

This makes it clearer that this stuff runs before any kind of exception,
and saves modifying PSTATE twice.

Signed-off-by: James Morse <james.morse@arm.com>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Cc: Julien Thierry <julien.thierry.kdev@gmail.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

1 files changed, 15 insertions, 3 deletions

diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-common.c
index 2c318e41d84b..5dce5e56995a 100644
--- a/arch/arm64/kernel/entry-common.c
+++ b/arch/arm64/kernel/entry-common.c
@@ -14,6 +14,7 @@
 #include <asm/esr.h>
 #include <asm/exception.h>
 #include <asm/kprobes.h>
+#include <asm/mmu.h>
 #include <asm/sysreg.h>
 
 static void notrace el1_abort(struct pt_regs *regs, unsigned long esr)
@@ -112,9 +113,17 @@ static void notrace el0_ia(struct pt_regs *regs, unsigned long esr)
 {
 	unsigned long far = read_sysreg(far_el1);
 
+	/*
+	 * We've taken an instruction abort from userspace and not yet
+	 * re-enabled IRQs. If the address is a kernel address, apply
+	 * BP hardening prior to enabling IRQs and pre-emption.
+	 */
+	if (!is_ttbr0_addr(far))
+		arm64_apply_bp_hardening();
+
 	user_exit_irqoff();
-	local_daif_restore(DAIF_PROCCTX_NOIRQ);
-	do_el0_ia_bp_hardening(far, esr, regs);
+	local_daif_restore(DAIF_PROCCTX);
+	do_mem_abort(far, esr, regs);
 }
 NOKPROBE_SYMBOL(el0_ia);
 
@@ -154,8 +163,11 @@ static void notrace el0_pc(struct pt_regs *regs, unsigned long esr)
 {
 	unsigned long far = read_sysreg(far_el1);
 
+	if (!is_ttbr0_addr(instruction_pointer(regs)))
+		arm64_apply_bp_hardening();
+
 	user_exit_irqoff();
-	local_daif_restore(DAIF_PROCCTX_NOIRQ);
+	local_daif_restore(DAIF_PROCCTX);
 	do_sp_pc_abort(far, esr, regs);
 }
 NOKPROBE_SYMBOL(el0_pc);