powerpc/kasan: Don't instrument non-maskable or raw interrupts

Disable address sanitization for raw and non-maskable interrupt
handlers, because they can run in real mode, where we cannot access
the shadow memory.  (Note that kasan_arch_is_ready() doesn't test for
real mode, since it is a static branch for speed, and in any case not
all the entry points to the generic KASAN code are protected by
kasan_arch_is_ready guards.)

The changes to interrupt_nmi_enter/exit_prepare() look larger than
they actually are.  The changes are equivalent to adding
!IS_ENABLED(CONFIG_KASAN) to the conditions for calling nmi_enter() or
nmi_exit() in real mode.  That is, the code is equivalent to using the
following condition for calling nmi_enter/exit:

	if (((!IS_ENABLED(CONFIG_PPC_BOOK3S_64) ||
			!firmware_has_feature(FW_FEATURE_LPAR) ||
			radix_enabled()) &&
		    !IS_ENABLED(CONFIG_KASAN) ||
		(mfmsr() & MSR_DR))

That unwieldy condition has been split into several statements with
comments, for easier reading.

The nmi_ipi_lock functions that call atomic functions (i.e.,
nmi_ipi_lock_start(), nmi_ipi_lock() and nmi_ipi_unlock()), besides
being marked noinstr, now call arch_atomic_* functions instead of
atomic_* functions because with KASAN enabled, the atomic_* functions
are wrappers which explicitly do address sanitization on their
arguments.  Since we are trying to avoid address sanitization, we have
to use the lower-level arch_atomic_* versions.

In hv_nmi_check_nonrecoverable(), the regs_set_unrecoverable() call
has been open-coded so as to avoid having to either trust the inlining
or mark regs_set_unrecoverable() as noinstr.

[paulus@ozlabs.org: combined a few work-in-progress commits of
 Daniel's and wrote the commit message.]

Signed-off-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/YoTFGaKM8Pd46PIK@cleo

2 files changed, 15 insertions, 13 deletions

diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index 4c4511b6a75d..4335efcb3184 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c
@@ -411,32 +411,32 @@ static struct cpumask nmi_ipi_pending_mask;
 static bool nmi_ipi_busy = false;
 static void (*nmi_ipi_function)(struct pt_regs *) = NULL;
 
-static void nmi_ipi_lock_start(unsigned long *flags)
+noinstr static void nmi_ipi_lock_start(unsigned long *flags)
 {
 	raw_local_irq_save(*flags);
 	hard_irq_disable();
-	while (atomic_cmpxchg(&__nmi_ipi_lock, 0, 1) == 1) {
+	while (arch_atomic_cmpxchg(&__nmi_ipi_lock, 0, 1) == 1) {
 		raw_local_irq_restore(*flags);
-		spin_until_cond(atomic_read(&__nmi_ipi_lock) == 0);
+		spin_until_cond(arch_atomic_read(&__nmi_ipi_lock) == 0);
 		raw_local_irq_save(*flags);
 		hard_irq_disable();
 	}
 }
 
-static void nmi_ipi_lock(void)
+noinstr static void nmi_ipi_lock(void)
 {
-	while (atomic_cmpxchg(&__nmi_ipi_lock, 0, 1) == 1)
-		spin_until_cond(atomic_read(&__nmi_ipi_lock) == 0);
+	while (arch_atomic_cmpxchg(&__nmi_ipi_lock, 0, 1) == 1)
+		spin_until_cond(arch_atomic_read(&__nmi_ipi_lock) == 0);
 }
 
-static void nmi_ipi_unlock(void)
+noinstr static void nmi_ipi_unlock(void)
 {
 	smp_mb();
-	WARN_ON(atomic_read(&__nmi_ipi_lock) != 1);
-	atomic_set(&__nmi_ipi_lock, 0);
+	WARN_ON(arch_atomic_read(&__nmi_ipi_lock) != 1);
+	arch_atomic_set(&__nmi_ipi_lock, 0);
 }
 
-static void nmi_ipi_unlock_end(unsigned long *flags)
+noinstr static void nmi_ipi_unlock_end(unsigned long *flags)
 {
 	nmi_ipi_unlock();
 	raw_local_irq_restore(*flags);
@@ -445,7 +445,7 @@ static void nmi_ipi_unlock_end(unsigned long *flags)
 /*
  * Platform NMI handler calls this to ack
  */
-int smp_handle_nmi_ipi(struct pt_regs *regs)
+noinstr int smp_handle_nmi_ipi(struct pt_regs *regs)
 {
 	void (*fn)(struct pt_regs *) = NULL;
 	unsigned long flags;
diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index a08bb7cefdc5..3aaa50e5c72f 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -393,7 +393,7 @@ void _exception(int signr, struct pt_regs *regs, int code, unsigned long addr)
  * Builds that do not support KVM could take this second option to increase
  * the recoverability of NMIs.
  */
-void hv_nmi_check_nonrecoverable(struct pt_regs *regs)
+noinstr void hv_nmi_check_nonrecoverable(struct pt_regs *regs)
 {
 #ifdef CONFIG_PPC_POWERNV
 	unsigned long kbase = (unsigned long)_stext;
@@ -433,7 +433,9 @@ void hv_nmi_check_nonrecoverable(struct pt_regs *regs)
 	return;
 
 nonrecoverable:
-	regs_set_unrecoverable(regs);
+	regs->msr &= ~MSR_RI;
+	local_paca->hsrr_valid = 0;
+	local_paca->srr_valid = 0;
 #endif
 }
 DEFINE_INTERRUPT_HANDLER_NMI(system_reset_exception)