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From: Mark Brown <broonie@kernel.org>
To: Catalin Marinas <catalin.marinas@arm.com>,
	 Will Deacon <will@kernel.org>, Jonathan Corbet <corbet@lwn.net>,
	 Andrew Morton <akpm@linux-foundation.org>,
	Marc Zyngier <maz@kernel.org>,
	 Oliver Upton <oliver.upton@linux.dev>,
	James Morse <james.morse@arm.com>,
	 Suzuki K Poulose <suzuki.poulose@arm.com>,
	Arnd Bergmann <arnd@arndb.de>,  Oleg Nesterov <oleg@redhat.com>,
	Eric Biederman <ebiederm@xmission.com>,
	 Kees Cook <keescook@chromium.org>, Shuah Khan <shuah@kernel.org>,
	 "Rick P. Edgecombe" <rick.p.edgecombe@intel.com>,
	 Deepak Gupta <debug@rivosinc.com>,
	Ard Biesheuvel <ardb@kernel.org>,
	 Szabolcs Nagy <Szabolcs.Nagy@arm.com>
Cc: "H.J. Lu" <hjl.tools@gmail.com>,
	 Paul Walmsley <paul.walmsley@sifive.com>,
	 Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	 linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org,
	 kvmarm@lists.linux.dev, linux-fsdevel@vger.kernel.org,
	 linux-arch@vger.kernel.org, linux-mm@kvack.org,
	 linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org,
	 linux-riscv@lists.infradead.org, Mark Brown <broonie@kernel.org>
Subject: [PATCH v2 20/35] arm64/gcs: Implement shadow stack prctl() interface
Date: Mon, 24 Jul 2023 13:46:07 +0100	[thread overview]
Message-ID: <20230724-arm64-gcs-v2-20-dc2c1d44c2eb@kernel.org> (raw)
In-Reply-To: <20230724-arm64-gcs-v2-0-dc2c1d44c2eb@kernel.org>

Implement the architecture neutral prtctl() interface for setting the
shadow stack status, this supports setting and reading the current GCS
configuration for the current thread.

Userspace can enable basic GCS functionality and additionally also
support for GCS pushes and arbatrary GCS stores.  It is expected that
this prctl() will be called very early in application startup, for
example by the dynamic linker, and not subsequently adjusted during
normal operation.  Users should carefully note that after enabling GCS
for a thread GCS will become active with no call stack so it is not
normally possible to return from the function that invoked the prctl().

State is stored per thread, enabling GCS for a thread causes a GCS to be
allocated for that thread.

Userspace may lock the current GCS configuration by specifying
PR_SHADOW_STACK_ENABLE_LOCK, this prevents any further changes to the
GCS configuration via any means.

If GCS is not being enabled then all flags other than _LOCK are ignored,
it is not possible to enable stores or pops without enabling GCS.

When disabling the GCS we do not free the allocated stack, this allows
for inspection of the GCS after disabling as part of fault reporting.
Since it is not an expected use case and since it presents some
complications in determining what to do with previously initialsed data
on the GCS attempts to reenable GCS after this are rejected.  This can
be revisted if a use case arises.

Signed-off-by: Mark Brown <broonie@kernel.org>
---
 arch/arm64/include/asm/gcs.h       | 22 ++++++++++
 arch/arm64/include/asm/processor.h |  1 +
 arch/arm64/mm/gcs.c                | 82 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 105 insertions(+)

diff --git a/arch/arm64/include/asm/gcs.h b/arch/arm64/include/asm/gcs.h
index 4371a2f99b4a..c150e76869a1 100644
--- a/arch/arm64/include/asm/gcs.h
+++ b/arch/arm64/include/asm/gcs.h
@@ -48,6 +48,9 @@ static inline u64 gcsss2(void)
 	return Xt;
 }
 
+#define PR_SHADOW_STACK_SUPPORTED_STATUS_MASK \
+	(PR_SHADOW_STACK_ENABLE | PR_SHADOW_STACK_WRITE | PR_SHADOW_STACK_PUSH)
+
 #ifdef CONFIG_ARM64_GCS
 
 static inline bool task_gcs_el0_enabled(struct task_struct *task)
@@ -61,6 +64,20 @@ void gcs_preserve_current_state(void);
 unsigned long gcs_alloc_thread_stack(struct task_struct *tsk,
 			    unsigned long clone_flags, size_t size);
 
+static inline int gcs_check_locked(struct task_struct *task,
+				   unsigned long new_val)
+{
+	unsigned long cur_val = task->thread.gcs_el0_mode;
+
+	cur_val &= task->thread.gcs_el0_locked;
+	new_val &= task->thread.gcs_el0_locked;
+
+	if (cur_val != new_val)
+		return -EBUSY;
+
+	return 0;
+}
+
 #else
 
 static inline bool task_gcs_el0_enabled(struct task_struct *task)
@@ -76,6 +93,11 @@ static inline unsigned long gcs_alloc_thread_stack(struct task_struct *tsk,
 {
 	return -ENOTSUPP;
 }
+static inline int gcs_check_locked(struct task_struct *task,
+				   unsigned long new_val)
+{
+	return 0;
+}
 
 #endif
 
diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
index f1551228a143..e4255749844a 100644
--- a/arch/arm64/include/asm/processor.h
+++ b/arch/arm64/include/asm/processor.h
@@ -181,6 +181,7 @@ struct thread_struct {
 	u64			tpidr2_el0;
 #ifdef CONFIG_ARM64_GCS
 	unsigned int		gcs_el0_mode;
+	unsigned int		gcs_el0_locked;
 	u64			gcspr_el0;
 	u64			gcs_base;
 	u64			gcs_size;
diff --git a/arch/arm64/mm/gcs.c b/arch/arm64/mm/gcs.c
index 1e059c37088d..64c9f9a85925 100644
--- a/arch/arm64/mm/gcs.c
+++ b/arch/arm64/mm/gcs.c
@@ -93,3 +93,85 @@ void gcs_free(struct task_struct *task)
 	task->thread.gcs_base = 0;
 	task->thread.gcs_size = 0;
 }
+
+int arch_set_shadow_stack_status(struct task_struct *task, unsigned long arg)
+{
+	unsigned long gcs, size;
+	int ret;
+
+	if (!system_supports_gcs())
+		return -EINVAL;
+
+	if (is_compat_thread(task_thread_info(task)))
+		return -EINVAL;
+
+	/* Reject unknown flags */
+	if (arg & ~PR_SHADOW_STACK_SUPPORTED_STATUS_MASK)
+		return -EINVAL;
+
+	ret = gcs_check_locked(task, arg);
+	if (ret != 0)
+		return ret;
+
+	/* If we are enabling GCS then make sure we have a stack */
+	if (arg & PR_SHADOW_STACK_ENABLE) {
+		if (!task_gcs_el0_enabled(task)) {
+			/* Do not allow GCS to be reenabled */
+			if (task->thread.gcs_base)
+				return -EINVAL;
+
+			if (task != current)
+				return -EBUSY;
+
+			size = gcs_size(0);
+			gcs = alloc_gcs(task->thread.gcspr_el0, size,
+					0, 0);
+			if (!gcs)
+				return -ENOMEM;
+
+			task->thread.gcspr_el0 = gcs + size - sizeof(u64);
+			task->thread.gcs_base = gcs;
+			task->thread.gcs_size = size;
+			if (task == current)
+				write_sysreg_s(task->thread.gcspr_el0,
+					       SYS_GCSPR_EL0);
+
+		}
+	}
+
+	task->thread.gcs_el0_mode = arg;
+	if (task == current)
+		gcs_set_el0_mode(task);
+
+	return 0;
+}
+
+int arch_get_shadow_stack_status(struct task_struct *task,
+				 unsigned long __user *arg)
+{
+	if (!system_supports_gcs())
+		return -EINVAL;
+
+	if (is_compat_thread(task_thread_info(task)))
+		return -EINVAL;
+
+	return put_user(task->thread.gcs_el0_mode, arg);
+}
+
+int arch_lock_shadow_stack_status(struct task_struct *task,
+				  unsigned long arg)
+{
+	if (!system_supports_gcs())
+		return -EINVAL;
+
+	if (is_compat_thread(task_thread_info(task)))
+		return -EINVAL;
+
+	/*
+	 * We support locking unknown bits so applications can prevent
+	 * any changes in a future proof manner.
+	 */
+	task->thread.gcs_el0_locked |= arg;
+
+	return 0;
+}

-- 
2.30.2


_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv

WARNING: multiple messages have this Message-ID (diff)
From: Mark Brown <broonie@kernel.org>
To: Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>, Jonathan Corbet <corbet@lwn.net>,
	Andrew Morton <akpm@linux-foundation.org>,
	Marc Zyngier <maz@kernel.org>,
	Oliver Upton <oliver.upton@linux.dev>,
	James Morse <james.morse@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Arnd Bergmann <arnd@arndb.de>, Oleg Nesterov <oleg@redhat.com>,
	Eric Biederman <ebiederm@xmission.com>,
	Kees Cook <keescook@chromium.org>, Shuah Khan <shuah@kernel.org>,
	"Rick P. Edgecombe" <rick.p.edgecombe@intel.com>,
	Deepak Gupta <debug@rivosinc.com>,
	Ard Biesheuvel <ardb@kernel.org>,
	Szabolcs Nagy <Szabolcs.Nagy@arm.com>
Cc: "H.J. Lu" <hjl.tools@gmail.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org,
	kvmarm@lists.linux.dev, linux-fsdevel@vger.kernel.org,
	linux-arch@vger.kernel.org, linux-mm@kvack.org,
	linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-riscv@lists.infradead.org, Mark Brown <broonie@kernel.org>
Subject: [PATCH v2 20/35] arm64/gcs: Implement shadow stack prctl() interface
Date: Mon, 24 Jul 2023 13:46:07 +0100	[thread overview]
Message-ID: <20230724-arm64-gcs-v2-20-dc2c1d44c2eb@kernel.org> (raw)
In-Reply-To: <20230724-arm64-gcs-v2-0-dc2c1d44c2eb@kernel.org>

Implement the architecture neutral prtctl() interface for setting the
shadow stack status, this supports setting and reading the current GCS
configuration for the current thread.

Userspace can enable basic GCS functionality and additionally also
support for GCS pushes and arbatrary GCS stores.  It is expected that
this prctl() will be called very early in application startup, for
example by the dynamic linker, and not subsequently adjusted during
normal operation.  Users should carefully note that after enabling GCS
for a thread GCS will become active with no call stack so it is not
normally possible to return from the function that invoked the prctl().

State is stored per thread, enabling GCS for a thread causes a GCS to be
allocated for that thread.

Userspace may lock the current GCS configuration by specifying
PR_SHADOW_STACK_ENABLE_LOCK, this prevents any further changes to the
GCS configuration via any means.

If GCS is not being enabled then all flags other than _LOCK are ignored,
it is not possible to enable stores or pops without enabling GCS.

When disabling the GCS we do not free the allocated stack, this allows
for inspection of the GCS after disabling as part of fault reporting.
Since it is not an expected use case and since it presents some
complications in determining what to do with previously initialsed data
on the GCS attempts to reenable GCS after this are rejected.  This can
be revisted if a use case arises.

Signed-off-by: Mark Brown <broonie@kernel.org>
---
 arch/arm64/include/asm/gcs.h       | 22 ++++++++++
 arch/arm64/include/asm/processor.h |  1 +
 arch/arm64/mm/gcs.c                | 82 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 105 insertions(+)

diff --git a/arch/arm64/include/asm/gcs.h b/arch/arm64/include/asm/gcs.h
index 4371a2f99b4a..c150e76869a1 100644
--- a/arch/arm64/include/asm/gcs.h
+++ b/arch/arm64/include/asm/gcs.h
@@ -48,6 +48,9 @@ static inline u64 gcsss2(void)
 	return Xt;
 }
 
+#define PR_SHADOW_STACK_SUPPORTED_STATUS_MASK \
+	(PR_SHADOW_STACK_ENABLE | PR_SHADOW_STACK_WRITE | PR_SHADOW_STACK_PUSH)
+
 #ifdef CONFIG_ARM64_GCS
 
 static inline bool task_gcs_el0_enabled(struct task_struct *task)
@@ -61,6 +64,20 @@ void gcs_preserve_current_state(void);
 unsigned long gcs_alloc_thread_stack(struct task_struct *tsk,
 			    unsigned long clone_flags, size_t size);
 
+static inline int gcs_check_locked(struct task_struct *task,
+				   unsigned long new_val)
+{
+	unsigned long cur_val = task->thread.gcs_el0_mode;
+
+	cur_val &= task->thread.gcs_el0_locked;
+	new_val &= task->thread.gcs_el0_locked;
+
+	if (cur_val != new_val)
+		return -EBUSY;
+
+	return 0;
+}
+
 #else
 
 static inline bool task_gcs_el0_enabled(struct task_struct *task)
@@ -76,6 +93,11 @@ static inline unsigned long gcs_alloc_thread_stack(struct task_struct *tsk,
 {
 	return -ENOTSUPP;
 }
+static inline int gcs_check_locked(struct task_struct *task,
+				   unsigned long new_val)
+{
+	return 0;
+}
 
 #endif
 
diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
index f1551228a143..e4255749844a 100644
--- a/arch/arm64/include/asm/processor.h
+++ b/arch/arm64/include/asm/processor.h
@@ -181,6 +181,7 @@ struct thread_struct {
 	u64			tpidr2_el0;
 #ifdef CONFIG_ARM64_GCS
 	unsigned int		gcs_el0_mode;
+	unsigned int		gcs_el0_locked;
 	u64			gcspr_el0;
 	u64			gcs_base;
 	u64			gcs_size;
diff --git a/arch/arm64/mm/gcs.c b/arch/arm64/mm/gcs.c
index 1e059c37088d..64c9f9a85925 100644
--- a/arch/arm64/mm/gcs.c
+++ b/arch/arm64/mm/gcs.c
@@ -93,3 +93,85 @@ void gcs_free(struct task_struct *task)
 	task->thread.gcs_base = 0;
 	task->thread.gcs_size = 0;
 }
+
+int arch_set_shadow_stack_status(struct task_struct *task, unsigned long arg)
+{
+	unsigned long gcs, size;
+	int ret;
+
+	if (!system_supports_gcs())
+		return -EINVAL;
+
+	if (is_compat_thread(task_thread_info(task)))
+		return -EINVAL;
+
+	/* Reject unknown flags */
+	if (arg & ~PR_SHADOW_STACK_SUPPORTED_STATUS_MASK)
+		return -EINVAL;
+
+	ret = gcs_check_locked(task, arg);
+	if (ret != 0)
+		return ret;
+
+	/* If we are enabling GCS then make sure we have a stack */
+	if (arg & PR_SHADOW_STACK_ENABLE) {
+		if (!task_gcs_el0_enabled(task)) {
+			/* Do not allow GCS to be reenabled */
+			if (task->thread.gcs_base)
+				return -EINVAL;
+
+			if (task != current)
+				return -EBUSY;
+
+			size = gcs_size(0);
+			gcs = alloc_gcs(task->thread.gcspr_el0, size,
+					0, 0);
+			if (!gcs)
+				return -ENOMEM;
+
+			task->thread.gcspr_el0 = gcs + size - sizeof(u64);
+			task->thread.gcs_base = gcs;
+			task->thread.gcs_size = size;
+			if (task == current)
+				write_sysreg_s(task->thread.gcspr_el0,
+					       SYS_GCSPR_EL0);
+
+		}
+	}
+
+	task->thread.gcs_el0_mode = arg;
+	if (task == current)
+		gcs_set_el0_mode(task);
+
+	return 0;
+}
+
+int arch_get_shadow_stack_status(struct task_struct *task,
+				 unsigned long __user *arg)
+{
+	if (!system_supports_gcs())
+		return -EINVAL;
+
+	if (is_compat_thread(task_thread_info(task)))
+		return -EINVAL;
+
+	return put_user(task->thread.gcs_el0_mode, arg);
+}
+
+int arch_lock_shadow_stack_status(struct task_struct *task,
+				  unsigned long arg)
+{
+	if (!system_supports_gcs())
+		return -EINVAL;
+
+	if (is_compat_thread(task_thread_info(task)))
+		return -EINVAL;
+
+	/*
+	 * We support locking unknown bits so applications can prevent
+	 * any changes in a future proof manner.
+	 */
+	task->thread.gcs_el0_locked |= arg;
+
+	return 0;
+}

-- 
2.30.2


  parent reply	other threads:[~2023-07-24 12:50 UTC|newest]

Thread overview: 72+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-07-24 12:45 [PATCH v2 00/35] arm64/gcs: Provide support for GCS in userspace Mark Brown
2023-07-24 12:45 ` Mark Brown
2023-07-24 12:45 ` [PATCH v2 01/35] prctl: arch-agnostic prctl for shadow stack Mark Brown
2023-07-24 12:45   ` Mark Brown
2023-07-24 12:45 ` [PATCH v2 02/35] arm64: Document boot requirements for Guarded Control Stacks Mark Brown
2023-07-24 12:45   ` Mark Brown
2023-07-24 12:45 ` [PATCH v2 03/35] arm64/gcs: Document the ABI " Mark Brown
2023-07-24 12:45   ` Mark Brown
2023-07-24 12:45 ` [PATCH v2 04/35] arm64/sysreg: Add new system registers for GCS Mark Brown
2023-07-24 12:45   ` Mark Brown
2023-07-24 12:45 ` [PATCH v2 05/35] arm64/sysreg: Add definitions for architected GCS caps Mark Brown
2023-07-24 12:45   ` Mark Brown
2023-07-24 12:45 ` [PATCH v2 06/35] arm64/gcs: Add manual encodings of GCS instructions Mark Brown
2023-07-24 12:45   ` Mark Brown
2023-07-24 12:45 ` [PATCH v2 07/35] arm64/gcs: Provide copy_to_user_gcs() Mark Brown
2023-07-24 12:45   ` Mark Brown
2023-07-24 12:45 ` [PATCH v2 08/35] arm64/cpufeature: Runtime detection of Guarded Control Stack (GCS) Mark Brown
2023-07-24 12:45   ` Mark Brown
2023-07-24 12:45 ` [PATCH v2 09/35] arm64/mm: Allocate PIE slots for EL0 guarded control stack Mark Brown
2023-07-24 12:45   ` Mark Brown
2023-07-24 12:45 ` [PATCH v2 10/35] mm: Define VM_SHADOW_STACK for arm64 when we support GCS Mark Brown
2023-07-24 12:45   ` Mark Brown
2023-07-24 12:45 ` [PATCH v2 11/35] arm64/mm: Map pages for guarded control stack Mark Brown
2023-07-24 12:45   ` Mark Brown
2023-07-24 12:45 ` [PATCH v2 12/35] KVM: arm64: Manage GCS registers for guests Mark Brown
2023-07-24 12:45   ` Mark Brown
2023-07-24 12:46 ` [PATCH v2 13/35] arm64/el2_setup: Allow GCS usage at EL0 and EL1 Mark Brown
2023-07-24 12:46   ` Mark Brown
2023-07-24 12:46 ` [PATCH v2 14/35] arm64/idreg: Add overrride for GCS Mark Brown
2023-07-24 12:46   ` Mark Brown
2023-07-24 12:46 ` [PATCH v2 15/35] arm64/hwcap: Add hwcap " Mark Brown
2023-07-24 12:46   ` Mark Brown
2023-07-24 12:46 ` [PATCH v2 16/35] arm64/traps: Handle GCS exceptions Mark Brown
2023-07-24 12:46   ` Mark Brown
2023-07-24 12:46 ` [PATCH v2 17/35] arm64/mm: Handle GCS data aborts Mark Brown
2023-07-24 12:46   ` Mark Brown
2023-07-24 12:46 ` [PATCH v2 18/35] arm64/gcs: Context switch GCS registers for EL0 Mark Brown
2023-07-24 12:46   ` Mark Brown
2023-07-24 12:46 ` [PATCH v2 19/35] arm64/gcs: Allocate a new GCS for threads with GCS enabled Mark Brown
2023-07-24 12:46   ` Mark Brown
2023-07-24 12:46 ` Mark Brown [this message]
2023-07-24 12:46   ` [PATCH v2 20/35] arm64/gcs: Implement shadow stack prctl() interface Mark Brown
2023-07-24 12:46 ` [PATCH v2 21/35] arm64/mm: Implement map_shadow_stack() Mark Brown
2023-07-24 12:46   ` Mark Brown
2023-07-24 12:46 ` [PATCH v2 22/35] arm64/signal: Set up and restore the GCS context for signal handlers Mark Brown
2023-07-24 12:46   ` Mark Brown
2023-07-24 12:46 ` [PATCH v2 23/35] arm64/signal: Expose GCS state in signal frames Mark Brown
2023-07-24 12:46   ` Mark Brown
2023-07-24 12:46 ` [PATCH v2 24/35] arm64/ptrace: Expose GCS via ptrace and core files Mark Brown
2023-07-24 12:46   ` Mark Brown
2023-07-24 12:46 ` [PATCH v2 25/35] arm64: Add Kconfig for Guarded Control Stack (GCS) Mark Brown
2023-07-24 12:46   ` Mark Brown
2023-07-24 12:46 ` [PATCH v2 26/35] kselftest/arm64: Verify the GCS hwcap Mark Brown
2023-07-24 12:46   ` Mark Brown
2023-07-24 12:46 ` [PATCH v2 27/35] kselftest/arm64: Add GCS as a detected feature in the signal tests Mark Brown
2023-07-24 12:46   ` Mark Brown
2023-07-24 12:46 ` [PATCH v2 28/35] kselftest/arm64: Add framework support for GCS to signal handling tests Mark Brown
2023-07-24 12:46   ` Mark Brown
2023-07-24 12:46 ` [PATCH v2 29/35] kselftest/arm64: Allow signals tests to specify an expected si_code Mark Brown
2023-07-24 12:46   ` Mark Brown
2023-07-24 12:46 ` [PATCH v2 30/35] kselftest/arm64: Always run signals tests with GCS enabled Mark Brown
2023-07-24 12:46   ` Mark Brown
2023-07-24 12:46 ` [PATCH v2 31/35] kselftest/arm64: Add very basic GCS test program Mark Brown
2023-07-24 12:46   ` Mark Brown
2023-07-24 12:46 ` [PATCH v2 32/35] kselftest/arm64: Add a GCS test program built with the system libc Mark Brown
2023-07-24 12:46   ` Mark Brown
2023-07-24 12:46 ` [PATCH v2 33/35] kselftest/arm64: Add test coverage for GCS mode locking Mark Brown
2023-07-24 12:46   ` Mark Brown
2023-07-24 12:46 ` [PATCH v2 34/35] selftests/arm64: Add GCS signal tests Mark Brown
2023-07-24 12:46   ` Mark Brown
2023-07-24 12:46 ` [PATCH v2 35/35] kselftest/arm64: Enable GCS for the FP stress tests Mark Brown
2023-07-24 12:46   ` Mark Brown

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