Commit caecde11 authored by Breno Leitao's avatar Breno Leitao Committed by Catalin Marinas
Browse files

arm64/irqflags: __always_inline the arch_local_irq_*() helpers 



The arch_local_irq_*() wrappers in <asm/irqflags.h> dispatch between two
underlying primitives: the __daif_* path on most systems, and the
__pmr_* path on builds that use GIC PMR-based masking (Pseudo-NMI). The
leaf primitives are already __always_inline, but the wrappers themselves
are plain "static inline".

That is unsafe for noinstr callers: nothing prevents the compiler from
emitting an out-of-line copy of e.g. arch_local_irq_disable(), and an
out-of-line copy can be instrumented (ftrace, kcov, sanitizers), which
breaks the noinstr contract on the entry/idle paths that rely on these
helpers.

x86 hit and fixed exactly this class of bug in commit 7a745be1
("x86/entry: __always_inline irqflags for noinstr").

Force-inline all of the arch_local_irq_*() wrappers so they cannot be
emitted out-of-line:

  - arch_local_irq_enable()
  - arch_local_irq_disable()
  - arch_local_save_flags()
  - arch_irqs_disabled_flags()
  - arch_irqs_disabled()
  - arch_local_irq_save()
  - arch_local_irq_restore()

The primary motivation is noinstr safety. There is a useful side effect
for fleet-wide profiling: when the wrapper is emitted out-of-line,
samples taken inside it during the post-WFI IRQ unmask in
default_idle_call() are attributed to arch_local_irq_enable rather than
default_idle_call(), and the FP-unwinder loses default_idle_call() from
the chain.

Signed-off-by: default avatarBreno Leitao <leitao@debian.org>
Reviewed-by: default avatarLeonardo Bras <leo.bras@arm.com>
Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent 4023b742

arch/arm64/include/asm/irqflags.h

+7 −7
Original line number Diff line number Diff line
@@ -40,7 +40,7 @@ static __always_inline void __pmr_local_irq_enable(void) 
	barrier();

}



static inline void arch_local_irq_enable(void)

static __always_inline void arch_local_irq_enable(void)

{

	if (system_uses_irq_prio_masking()) {

		__pmr_local_irq_enable();
@@ -68,7 +68,7 @@ static __always_inline void __pmr_local_irq_disable(void) 
	barrier();

}



static inline void arch_local_irq_disable(void)

static __always_inline void arch_local_irq_disable(void)

{

	if (system_uses_irq_prio_masking()) {

		__pmr_local_irq_disable();
@@ -90,7 +90,7 @@ static __always_inline unsigned long __pmr_local_save_flags(void) 
/*

 * Save the current interrupt enable state.

 */

static inline unsigned long arch_local_save_flags(void)

static __always_inline unsigned long arch_local_save_flags(void)

{

	if (system_uses_irq_prio_masking()) {

		return __pmr_local_save_flags();
@@ -109,7 +109,7 @@ static __always_inline bool __pmr_irqs_disabled_flags(unsigned long flags) 
	return flags != GIC_PRIO_IRQON;

}



static inline bool arch_irqs_disabled_flags(unsigned long flags)

static __always_inline bool arch_irqs_disabled_flags(unsigned long flags)

{

	if (system_uses_irq_prio_masking()) {

		return __pmr_irqs_disabled_flags(flags);
@@ -128,7 +128,7 @@ static __always_inline bool __pmr_irqs_disabled(void) 
	return __pmr_irqs_disabled_flags(__pmr_local_save_flags());

}



static inline bool arch_irqs_disabled(void)

static __always_inline bool arch_irqs_disabled(void)

{

	if (system_uses_irq_prio_masking()) {

		return __pmr_irqs_disabled();
@@ -160,7 +160,7 @@ static __always_inline unsigned long __pmr_local_irq_save(void) 
	return flags;

}



static inline unsigned long arch_local_irq_save(void)

static __always_inline unsigned long arch_local_irq_save(void)

{

	if (system_uses_irq_prio_masking()) {

		return __pmr_local_irq_save();
@@ -187,7 +187,7 @@ static __always_inline void __pmr_local_irq_restore(unsigned long flags) 
/*

 * restore saved IRQ state

 */

static inline void arch_local_irq_restore(unsigned long flags)

static __always_inline void arch_local_irq_restore(unsigned long flags)

{

	if (system_uses_irq_prio_masking()) {

		__pmr_local_irq_restore(flags);