linux-kernel - [PATCH v9 12/39] arm64/mm: Map pages for guarded control stack

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Message-Id: <20240625-arm64-gcs-v9-12-0f634469b8f0@kernel.org>
Date: Tue, 25 Jun 2024 15:57:40 +0100
From: Mark Brown <broonie@...nel.org>
To: Catalin Marinas <catalin.marinas@....com>, 
 Will Deacon <will@...nel.org>, Jonathan Corbet <corbet@....net>, 
 Andrew Morton <akpm@...ux-foundation.org>, Marc Zyngier <maz@...nel.org>, 
 Oliver Upton <oliver.upton@...ux.dev>, James Morse <james.morse@....com>, 
 Suzuki K Poulose <suzuki.poulose@....com>, Arnd Bergmann <arnd@...db.de>, 
 Oleg Nesterov <oleg@...hat.com>, Eric Biederman <ebiederm@...ssion.com>, 
 Shuah Khan <shuah@...nel.org>, 
 "Rick P. Edgecombe" <rick.p.edgecombe@...el.com>, 
 Deepak Gupta <debug@...osinc.com>, Ard Biesheuvel <ardb@...nel.org>, 
 Szabolcs Nagy <Szabolcs.Nagy@....com>, Kees Cook <kees@...nel.org>
Cc: "H.J. Lu" <hjl.tools@...il.com>, 
 Paul Walmsley <paul.walmsley@...ive.com>, 
 Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, 
 Florian Weimer <fweimer@...hat.com>, Christian Brauner <brauner@...nel.org>, 
 Thiago Jung Bauermann <thiago.bauermann@...aro.org>, 
 Ross Burton <ross.burton@....com>, linux-arm-kernel@...ts.infradead.org, 
 linux-doc@...r.kernel.org, kvmarm@...ts.linux.dev, 
 linux-fsdevel@...r.kernel.org, linux-arch@...r.kernel.org, 
 linux-mm@...ck.org, linux-kselftest@...r.kernel.org, 
 linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org, 
 Mark Brown <broonie@...nel.org>
Subject: [PATCH v9 12/39] arm64/mm: Map pages for guarded control stack

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@...aro.org>
Signed-off-by: Mark Brown <broonie@...nel.org>
---
 arch/arm64/include/asm/mman.h |  9 +++++++++
 arch/arm64/mm/mmap.c          | 13 ++++++++++++-
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/mman.h b/arch/arm64/include/asm/mman.h
index c21849ffdd88..6d3fe6433a62 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, and the mm
+		 * core can't cope with a shared GCS.
+		 */
+		if (vm_flags & (VM_EXEC | VM_ARM64_BTI | VM_SHARED))
+			return false;
+	}
+
 	return true;

 }
diff --git a/arch/arm64/mm/mmap.c b/arch/arm64/mm/mmap.c
index 642bdf908b22..68a17bd09d00 100644
--- a/arch/arm64/mm/mmap.c
+++ b/arch/arm64/mm/mmap.c
@@ -83,9 +83,20 @@ 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;
+
+	/* If this is a GCS then only interpret VM_WRITE. */
+	if (system_supports_gcs() && (vm_flags & VM_SHADOW_STACK)) {
+		if (vm_flags & VM_WRITE)
+			prot = _PAGE_GCS;
+		else
+			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;

-- 
2.39.2