diff mbox series

[v11,14/39] arm64/mm: Map pages for guarded control stack

Message ID 20240822-arm64-gcs-v11-14-41b81947ecb5@kernel.org
State Superseded
Headers show
Series arm64/gcs: Provide support for GCS in userspace | expand

Commit Message

Mark Brown Aug. 22, 2024, 1:15 a.m. UTC 
Map pages flagged as being part of a GCS as such rather than using the
full set of generic VM flags.

This is done using a conditional rather than extending the size of
protection_map since that would make for a very sparse array.

Reviewed-by: Thiago Jung Bauermann <thiago.bauermann@linaro.org>
Signed-off-by: Mark Brown <broonie@kernel.org>
---
 arch/arm64/include/asm/mman.h |  9 +++++++++
 arch/arm64/mm/mmap.c          | 10 +++++++++-
 2 files changed, 18 insertions(+), 1 deletion(-)

Comments

Catalin Marinas Aug. 22, 2024, 10:19 a.m. UTC | #1 
On Thu, Aug 22, 2024 at 02:15:17AM +0100, Mark Brown wrote:
> diff --git a/arch/arm64/include/asm/mman.h b/arch/arm64/include/asm/mman.h
> index c21849ffdd88..37dfd2882f04 100644
> --- a/arch/arm64/include/asm/mman.h
> +++ b/arch/arm64/include/asm/mman.h
> @@ -61,6 +61,15 @@ static inline bool arch_validate_flags(unsigned long vm_flags)
>  			return false;
>  	}
>  
> +	if (system_supports_gcs() && (vm_flags & VM_SHADOW_STACK)) {
> +		/* An executable GCS isn't a good idea. */
> +		if (vm_flags & VM_EXEC)
> +			return false;

Later we should look at clear VM_MAYEXEC in the core code (if the x86
folk agree).

> +
> +		/* The memory management core should prevent this */
> +		VM_WARN_ON(vm_flags & VM_SHARED);
> +	}
> +
>  	return true;
>  
>  }
> diff --git a/arch/arm64/mm/mmap.c b/arch/arm64/mm/mmap.c
> index 642bdf908b22..3ed63fc8cd0a 100644
> --- a/arch/arm64/mm/mmap.c
> +++ b/arch/arm64/mm/mmap.c
> @@ -83,9 +83,17 @@ arch_initcall(adjust_protection_map);
>  
>  pgprot_t vm_get_page_prot(unsigned long vm_flags)
>  {
> -	pteval_t prot = pgprot_val(protection_map[vm_flags &
> +	pteval_t prot;
> +
> +	/* Short circuit GCS to avoid bloating the table. */
> +	if (system_supports_gcs() && (vm_flags & VM_SHADOW_STACK)) {
> +		prot = _PAGE_GCS_RO;
> +	} else {
> +		prot = pgprot_val(protection_map[vm_flags &
>  				   (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)]);
> +	}
>  
> +	/* VM_ARM64_BTI on a GCS is rejected in arch_validate_flags() */

Not anymore.

>  	if (vm_flags & VM_ARM64_BTI)
>  		prot |= PTE_GP;

Other than the comment above, it looks good.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
diff mbox series

Patch

diff --git a/arch/arm64/include/asm/mman.h b/arch/arm64/include/asm/mman.h
index c21849ffdd88..37dfd2882f04 100644
--- a/arch/arm64/include/asm/mman.h
+++ b/arch/arm64/include/asm/mman.h
@@ -61,6 +61,15 @@  static inline bool arch_validate_flags(unsigned long vm_flags)
 			return false;
 	}
 
+	if (system_supports_gcs() && (vm_flags & VM_SHADOW_STACK)) {
+		/* An executable GCS isn't a good idea. */
+		if (vm_flags & VM_EXEC)
+			return false;
+
+		/* The memory management core should prevent this */
+		VM_WARN_ON(vm_flags & VM_SHARED);
+	}
+
 	return true;
 
 }
diff --git a/arch/arm64/mm/mmap.c b/arch/arm64/mm/mmap.c
index 642bdf908b22..3ed63fc8cd0a 100644
--- a/arch/arm64/mm/mmap.c
+++ b/arch/arm64/mm/mmap.c
@@ -83,9 +83,17 @@  arch_initcall(adjust_protection_map);
 
 pgprot_t vm_get_page_prot(unsigned long vm_flags)
 {
-	pteval_t prot = pgprot_val(protection_map[vm_flags &
+	pteval_t prot;
+
+	/* Short circuit GCS to avoid bloating the table. */
+	if (system_supports_gcs() && (vm_flags & VM_SHADOW_STACK)) {
+		prot = _PAGE_GCS_RO;
+	} else {
+		prot = pgprot_val(protection_map[vm_flags &
 				   (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)]);
+	}
 
+	/* VM_ARM64_BTI on a GCS is rejected in arch_validate_flags() */
 	if (vm_flags & VM_ARM64_BTI)
 		prot |= PTE_GP;