[PATCH] arm64: make is_ttbrX_addr() noinstr-safe

[PATCH] arm64: make is_ttbrX_addr() noinstr-safe

[Mark Rutland]

We use is_ttbr0_addr() in noinstr code, but as it's only marked as
inline, it's theoretically possible for the compiler to place it
out-of-line and instrument it, which would be problematic.

Mark is_ttbr0_addr() as __always_inline such that that can safely be
used from noinstr code. For consistency, do the same to is_ttbr1_addr().
Note that while is_ttbr1_addr() calls arch_kasan_reset_tag(), this is a
macro (and its callees are either macros or __always_inline), so there
is not a risk of transient instrumentation.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
---
 arch/arm64/include/asm/processor.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
index 445aa3af3b76..400f8956328b 100644
--- a/arch/arm64/include/asm/processor.h
+++ b/arch/arm64/include/asm/processor.h
@@ -308,13 +308,13 @@ static inline void compat_start_thread(struct pt_regs *regs, unsigned long pc,
 }
 #endif
 
-static inline bool is_ttbr0_addr(unsigned long addr)
+static __always_inline bool is_ttbr0_addr(unsigned long addr)
 {
 	/* entry assembly clears tags for TTBR0 addrs */
 	return addr < TASK_SIZE;
 }
 
-static inline bool is_ttbr1_addr(unsigned long addr)
+static __always_inline bool is_ttbr1_addr(unsigned long addr)
 {
 	/* TTBR1 addresses may have a tag if KASAN_SW_TAGS is in use */
 	return arch_kasan_reset_tag(addr) >= PAGE_OFFSET;
-- 
2.30.2


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Re: [PATCH] arm64: make is_ttbrX_addr() noinstr-safe

[Will Deacon]

On Mon, 14 Nov 2022 14:40:42 +0000, Mark Rutland wrote:
> We use is_ttbr0_addr() in noinstr code, but as it's only marked as
> inline, it's theoretically possible for the compiler to place it
> out-of-line and instrument it, which would be problematic.
> 
> Mark is_ttbr0_addr() as __always_inline such that that can safely be
> used from noinstr code. For consistency, do the same to is_ttbr1_addr().
> Note that while is_ttbr1_addr() calls arch_kasan_reset_tag(), this is a
> macro (and its callees are either macros or __always_inline), so there
> is not a risk of transient instrumentation.
> 
> [...]

Applied to arm64 (for-next/trivial), thanks!

[1/1] arm64: make is_ttbrX_addr() noinstr-safe
      https://git.kernel.org/arm64/c/d8c1d798a2e5

Cheers,
-- 
Will

https://fixes.arm64.dev
https://next.arm64.dev
https://will.arm64.dev

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