[v18,02/15] arm64: Introduce prctl() options to control the tagged user addresses ABI

Submitted by Andrey Konovalov on June 24, 2019, 2:32 p.m.

Details

Message ID 653598b3cfcd80f0cc69f72a214e156bb1afde68.1561386715.git.andreyknvl@google.com
State New
Headers show
Series "arm64: untag user pointers passed to the kernel" ( rev: 9 8 ) in AMD X.Org drivers

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Commit Message

Andrey Konovalov June 24, 2019, 2:32 p.m.
From: Catalin Marinas <catalin.marinas@arm.com>

It is not desirable to relax the ABI to allow tagged user addresses into
the kernel indiscriminately. This patch introduces a prctl() interface
for enabling or disabling the tagged ABI with a global sysctl control
for preventing applications from enabling the relaxed ABI (meant for
testing user-space prctl() return error checking without reconfiguring
the kernel). The ABI properties are inherited by threads of the same
application and fork()'ed children but cleared on execve(). A Kconfig
option allows the overall disabling of the relaxed ABI.

The PR_SET_TAGGED_ADDR_CTRL will be expanded in the future to handle
MTE-specific settings like imprecise vs precise exceptions.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 arch/arm64/Kconfig                   |  9 ++++
 arch/arm64/include/asm/processor.h   |  8 ++++
 arch/arm64/include/asm/thread_info.h |  1 +
 arch/arm64/include/asm/uaccess.h     |  4 +-
 arch/arm64/kernel/process.c          | 72 ++++++++++++++++++++++++++++
 include/uapi/linux/prctl.h           |  5 ++
 kernel/sys.c                         | 12 +++++
 7 files changed, 110 insertions(+), 1 deletion(-)

Patch hide | download patch | download mbox

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 697ea0510729..55fbaf20af2d 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -1107,6 +1107,15 @@  config ARM64_SW_TTBR0_PAN
 	  zeroed area and reserved ASID. The user access routines
 	  restore the valid TTBR0_EL1 temporarily.
 
+config ARM64_TAGGED_ADDR_ABI
+	bool "Enable the tagged user addresses syscall ABI"
+	default y
+	help
+	  When this option is enabled, user applications can opt in to a
+	  relaxed ABI via prctl() allowing tagged addresses to be passed
+	  to system calls as pointer arguments. For details, see
+	  Documentation/arm64/tagged-address-abi.txt.
+
 menuconfig COMPAT
 	bool "Kernel support for 32-bit EL0"
 	depends on ARM64_4K_PAGES || EXPERT
diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
index fd5b1a4efc70..ee86070a28d4 100644
--- a/arch/arm64/include/asm/processor.h
+++ b/arch/arm64/include/asm/processor.h
@@ -296,6 +296,14 @@  extern void __init minsigstksz_setup(void);
 /* PR_PAC_RESET_KEYS prctl */
 #define PAC_RESET_KEYS(tsk, arg)	ptrauth_prctl_reset_keys(tsk, arg)
 
+#ifdef CONFIG_ARM64_TAGGED_ADDR_ABI
+/* PR_{SET,GET}_TAGGED_ADDR_CTRL prctl */
+long set_tagged_addr_ctrl(unsigned long arg);
+long get_tagged_addr_ctrl(void);
+#define SET_TAGGED_ADDR_CTRL(arg)	set_tagged_addr_ctrl(arg)
+#define GET_TAGGED_ADDR_CTRL()		get_tagged_addr_ctrl()
+#endif
+
 /*
  * For CONFIG_GCC_PLUGIN_STACKLEAK
  *
diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h
index 2372e97db29c..4f81c4f15404 100644
--- a/arch/arm64/include/asm/thread_info.h
+++ b/arch/arm64/include/asm/thread_info.h
@@ -88,6 +88,7 @@  void arch_release_task_struct(struct task_struct *tsk);
 #define TIF_SVE			23	/* Scalable Vector Extension in use */
 #define TIF_SVE_VL_INHERIT	24	/* Inherit sve_vl_onexec across exec */
 #define TIF_SSBD		25	/* Wants SSB mitigation */
+#define TIF_TAGGED_ADDR		26	/* Allow tagged user addresses */
 
 #define _TIF_SIGPENDING		(1 << TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1 << TIF_NEED_RESCHED)
diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index a138e3b4f717..097d6bfac0b7 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -62,7 +62,9 @@  static inline unsigned long __range_ok(const void __user *addr, unsigned long si
 {
 	unsigned long ret, limit = current_thread_info()->addr_limit;
 
-	addr = untagged_addr(addr);
+	if (IS_ENABLED(CONFIG_ARM64_TAGGED_ADDR_ABI) &&
+	    test_thread_flag(TIF_TAGGED_ADDR))
+		addr = untagged_addr(addr);
 
 	__chk_user_ptr(addr);
 	asm volatile(
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 9856395ccdb7..60e70158a4a1 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -19,6 +19,7 @@ 
 #include <linux/kernel.h>
 #include <linux/mm.h>
 #include <linux/stddef.h>
+#include <linux/sysctl.h>
 #include <linux/unistd.h>
 #include <linux/user.h>
 #include <linux/delay.h>
@@ -307,11 +308,18 @@  static void tls_thread_flush(void)
 	}
 }
 
+static void flush_tagged_addr_state(void)
+{
+	if (IS_ENABLED(CONFIG_ARM64_TAGGED_ADDR_ABI))
+		clear_thread_flag(TIF_TAGGED_ADDR);
+}
+
 void flush_thread(void)
 {
 	fpsimd_flush_thread();
 	tls_thread_flush();
 	flush_ptrace_hw_breakpoint(current);
+	flush_tagged_addr_state();
 }
 
 void release_thread(struct task_struct *dead_task)
@@ -541,3 +549,67 @@  void arch_setup_new_exec(void)
 
 	ptrauth_thread_init_user(current);
 }
+
+#ifdef CONFIG_ARM64_TAGGED_ADDR_ABI
+/*
+ * Control the relaxed ABI allowing tagged user addresses into the kernel.
+ */
+static unsigned int tagged_addr_prctl_allowed = 1;
+
+long set_tagged_addr_ctrl(unsigned long arg)
+{
+	if (!tagged_addr_prctl_allowed)
+		return -EINVAL;
+	if (is_compat_task())
+		return -EINVAL;
+	if (arg & ~PR_TAGGED_ADDR_ENABLE)
+		return -EINVAL;
+
+	update_thread_flag(TIF_TAGGED_ADDR, arg & PR_TAGGED_ADDR_ENABLE);
+
+	return 0;
+}
+
+long get_tagged_addr_ctrl(void)
+{
+	if (!tagged_addr_prctl_allowed)
+		return -EINVAL;
+	if (is_compat_task())
+		return -EINVAL;
+
+	if (test_thread_flag(TIF_TAGGED_ADDR))
+		return PR_TAGGED_ADDR_ENABLE;
+
+	return 0;
+}
+
+/*
+ * Global sysctl to disable the tagged user addresses support. This control
+ * only prevents the tagged address ABI enabling via prctl() and does not
+ * disable it for tasks that already opted in to the relaxed ABI.
+ */
+static int zero;
+static int one = 1;
+
+static struct ctl_table tagged_addr_sysctl_table[] = {
+	{
+		.procname	= "tagged_addr",
+		.mode		= 0644,
+		.data		= &tagged_addr_prctl_allowed,
+		.maxlen		= sizeof(int),
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= &zero,
+		.extra2		= &one,
+	},
+	{ }
+};
+
+static int __init tagged_addr_init(void)
+{
+	if (!register_sysctl("abi", tagged_addr_sysctl_table))
+		return -EINVAL;
+	return 0;
+}
+
+core_initcall(tagged_addr_init);
+#endif	/* CONFIG_ARM64_TAGGED_ADDR_ABI */
diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
index 094bb03b9cc2..2e927b3e9d6c 100644
--- a/include/uapi/linux/prctl.h
+++ b/include/uapi/linux/prctl.h
@@ -229,4 +229,9 @@  struct prctl_mm_map {
 # define PR_PAC_APDBKEY			(1UL << 3)
 # define PR_PAC_APGAKEY			(1UL << 4)
 
+/* Tagged user address controls for arm64 */
+#define PR_SET_TAGGED_ADDR_CTRL		55
+#define PR_GET_TAGGED_ADDR_CTRL		56
+# define PR_TAGGED_ADDR_ENABLE		(1UL << 0)
+
 #endif /* _LINUX_PRCTL_H */
diff --git a/kernel/sys.c b/kernel/sys.c
index 2969304c29fe..c6c4d5358bd3 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -124,6 +124,12 @@ 
 #ifndef PAC_RESET_KEYS
 # define PAC_RESET_KEYS(a, b)	(-EINVAL)
 #endif
+#ifndef SET_TAGGED_ADDR_CTRL
+# define SET_TAGGED_ADDR_CTRL(a)	(-EINVAL)
+#endif
+#ifndef GET_TAGGED_ADDR_CTRL
+# define GET_TAGGED_ADDR_CTRL()		(-EINVAL)
+#endif
 
 /*
  * this is where the system-wide overflow UID and GID are defined, for
@@ -2492,6 +2498,12 @@  SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
 			return -EINVAL;
 		error = PAC_RESET_KEYS(me, arg2);
 		break;
+	case PR_SET_TAGGED_ADDR_CTRL:
+		error = SET_TAGGED_ADDR_CTRL(arg2);
+		break;
+	case PR_GET_TAGGED_ADDR_CTRL:
+		error = GET_TAGGED_ADDR_CTRL();
+		break;
 	default:
 		error = -EINVAL;
 		break;

Comments

On Mon, Jun 24, 2019 at 04:32:47PM +0200, Andrey Konovalov wrote:
> From: Catalin Marinas <catalin.marinas@arm.com>
> 
> It is not desirable to relax the ABI to allow tagged user addresses into
> the kernel indiscriminately. This patch introduces a prctl() interface
> for enabling or disabling the tagged ABI with a global sysctl control
> for preventing applications from enabling the relaxed ABI (meant for
> testing user-space prctl() return error checking without reconfiguring
> the kernel). The ABI properties are inherited by threads of the same
> application and fork()'ed children but cleared on execve(). A Kconfig
> option allows the overall disabling of the relaxed ABI.
> 
> The PR_SET_TAGGED_ADDR_CTRL will be expanded in the future to handle
> MTE-specific settings like imprecise vs precise exceptions.
> 
> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
> ---
>  arch/arm64/Kconfig                   |  9 ++++
>  arch/arm64/include/asm/processor.h   |  8 ++++
>  arch/arm64/include/asm/thread_info.h |  1 +
>  arch/arm64/include/asm/uaccess.h     |  4 +-
>  arch/arm64/kernel/process.c          | 72 ++++++++++++++++++++++++++++
>  include/uapi/linux/prctl.h           |  5 ++
>  kernel/sys.c                         | 12 +++++
>  7 files changed, 110 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 697ea0510729..55fbaf20af2d 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -1107,6 +1107,15 @@ config ARM64_SW_TTBR0_PAN
>  	  zeroed area and reserved ASID. The user access routines
>  	  restore the valid TTBR0_EL1 temporarily.
>  
> +config ARM64_TAGGED_ADDR_ABI
> +	bool "Enable the tagged user addresses syscall ABI"
> +	default y
> +	help
> +	  When this option is enabled, user applications can opt in to a
> +	  relaxed ABI via prctl() allowing tagged addresses to be passed
> +	  to system calls as pointer arguments. For details, see
> +	  Documentation/arm64/tagged-address-abi.txt.
> +
>  menuconfig COMPAT
>  	bool "Kernel support for 32-bit EL0"
>  	depends on ARM64_4K_PAGES || EXPERT
> diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
> index fd5b1a4efc70..ee86070a28d4 100644
> --- a/arch/arm64/include/asm/processor.h
> +++ b/arch/arm64/include/asm/processor.h
> @@ -296,6 +296,14 @@ extern void __init minsigstksz_setup(void);
>  /* PR_PAC_RESET_KEYS prctl */
>  #define PAC_RESET_KEYS(tsk, arg)	ptrauth_prctl_reset_keys(tsk, arg)
>  
> +#ifdef CONFIG_ARM64_TAGGED_ADDR_ABI
> +/* PR_{SET,GET}_TAGGED_ADDR_CTRL prctl */
> +long set_tagged_addr_ctrl(unsigned long arg);
> +long get_tagged_addr_ctrl(void);
> +#define SET_TAGGED_ADDR_CTRL(arg)	set_tagged_addr_ctrl(arg)
> +#define GET_TAGGED_ADDR_CTRL()		get_tagged_addr_ctrl()
> +#endif
> +
>  /*
>   * For CONFIG_GCC_PLUGIN_STACKLEAK
>   *
> diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h
> index 2372e97db29c..4f81c4f15404 100644
> --- a/arch/arm64/include/asm/thread_info.h
> +++ b/arch/arm64/include/asm/thread_info.h
> @@ -88,6 +88,7 @@ void arch_release_task_struct(struct task_struct *tsk);
>  #define TIF_SVE			23	/* Scalable Vector Extension in use */
>  #define TIF_SVE_VL_INHERIT	24	/* Inherit sve_vl_onexec across exec */
>  #define TIF_SSBD		25	/* Wants SSB mitigation */
> +#define TIF_TAGGED_ADDR		26	/* Allow tagged user addresses */
>  
>  #define _TIF_SIGPENDING		(1 << TIF_SIGPENDING)
>  #define _TIF_NEED_RESCHED	(1 << TIF_NEED_RESCHED)
> diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
> index a138e3b4f717..097d6bfac0b7 100644
> --- a/arch/arm64/include/asm/uaccess.h
> +++ b/arch/arm64/include/asm/uaccess.h
> @@ -62,7 +62,9 @@ static inline unsigned long __range_ok(const void __user *addr, unsigned long si
>  {
>  	unsigned long ret, limit = current_thread_info()->addr_limit;
>  
> -	addr = untagged_addr(addr);
> +	if (IS_ENABLED(CONFIG_ARM64_TAGGED_ADDR_ABI) &&
> +	    test_thread_flag(TIF_TAGGED_ADDR))
> +		addr = untagged_addr(addr);
>  
>  	__chk_user_ptr(addr);
>  	asm volatile(
> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
> index 9856395ccdb7..60e70158a4a1 100644
> --- a/arch/arm64/kernel/process.c
> +++ b/arch/arm64/kernel/process.c
> @@ -19,6 +19,7 @@
>  #include <linux/kernel.h>
>  #include <linux/mm.h>
>  #include <linux/stddef.h>
> +#include <linux/sysctl.h>
>  #include <linux/unistd.h>
>  #include <linux/user.h>
>  #include <linux/delay.h>
> @@ -307,11 +308,18 @@ static void tls_thread_flush(void)
>  	}
>  }
>  
> +static void flush_tagged_addr_state(void)
> +{
> +	if (IS_ENABLED(CONFIG_ARM64_TAGGED_ADDR_ABI))
> +		clear_thread_flag(TIF_TAGGED_ADDR);
> +}
> +
>  void flush_thread(void)
>  {
>  	fpsimd_flush_thread();
>  	tls_thread_flush();
>  	flush_ptrace_hw_breakpoint(current);
> +	flush_tagged_addr_state();
>  }
>  
>  void release_thread(struct task_struct *dead_task)
> @@ -541,3 +549,67 @@ void arch_setup_new_exec(void)
>  
>  	ptrauth_thread_init_user(current);
>  }
> +
> +#ifdef CONFIG_ARM64_TAGGED_ADDR_ABI
> +/*
> + * Control the relaxed ABI allowing tagged user addresses into the kernel.
> + */
> +static unsigned int tagged_addr_prctl_allowed = 1;
> +
> +long set_tagged_addr_ctrl(unsigned long arg)
> +{
> +	if (!tagged_addr_prctl_allowed)
> +		return -EINVAL;
> +	if (is_compat_task())
> +		return -EINVAL;
> +	if (arg & ~PR_TAGGED_ADDR_ENABLE)
> +		return -EINVAL;
> +
> +	update_thread_flag(TIF_TAGGED_ADDR, arg & PR_TAGGED_ADDR_ENABLE);
> +
> +	return 0;
> +}
> +
> +long get_tagged_addr_ctrl(void)
> +{
> +	if (!tagged_addr_prctl_allowed)
> +		return -EINVAL;
> +	if (is_compat_task())
> +		return -EINVAL;
> +
> +	if (test_thread_flag(TIF_TAGGED_ADDR))
> +		return PR_TAGGED_ADDR_ENABLE;
> +
> +	return 0;
> +}
> +
> +/*
> + * Global sysctl to disable the tagged user addresses support. This control
> + * only prevents the tagged address ABI enabling via prctl() and does not
> + * disable it for tasks that already opted in to the relaxed ABI.
> + */
> +static int zero;
> +static int one = 1;
> +
> +static struct ctl_table tagged_addr_sysctl_table[] = {
> +	{
> +		.procname	= "tagged_addr",
> +		.mode		= 0644,
> +		.data		= &tagged_addr_prctl_allowed,
> +		.maxlen		= sizeof(int),
> +		.proc_handler	= proc_dointvec_minmax,
> +		.extra1		= &zero,
> +		.extra2		= &one,
> +	},
> +	{ }
> +};
> +
> +static int __init tagged_addr_init(void)
> +{
> +	if (!register_sysctl("abi", tagged_addr_sysctl_table))
> +		return -EINVAL;
> +	return 0;
> +}
> +
> +core_initcall(tagged_addr_init);
> +#endif	/* CONFIG_ARM64_TAGGED_ADDR_ABI */
> diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
> index 094bb03b9cc2..2e927b3e9d6c 100644
> --- a/include/uapi/linux/prctl.h
> +++ b/include/uapi/linux/prctl.h
> @@ -229,4 +229,9 @@ struct prctl_mm_map {
>  # define PR_PAC_APDBKEY			(1UL << 3)
>  # define PR_PAC_APGAKEY			(1UL << 4)
>  
> +/* Tagged user address controls for arm64 */
> +#define PR_SET_TAGGED_ADDR_CTRL		55
> +#define PR_GET_TAGGED_ADDR_CTRL		56
> +# define PR_TAGGED_ADDR_ENABLE		(1UL << 0)
> +
>  #endif /* _LINUX_PRCTL_H */
> diff --git a/kernel/sys.c b/kernel/sys.c
> index 2969304c29fe..c6c4d5358bd3 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -124,6 +124,12 @@
>  #ifndef PAC_RESET_KEYS
>  # define PAC_RESET_KEYS(a, b)	(-EINVAL)
>  #endif
> +#ifndef SET_TAGGED_ADDR_CTRL
> +# define SET_TAGGED_ADDR_CTRL(a)	(-EINVAL)
> +#endif
> +#ifndef GET_TAGGED_ADDR_CTRL
> +# define GET_TAGGED_ADDR_CTRL()		(-EINVAL)
> +#endif
>  
>  /*
>   * this is where the system-wide overflow UID and GID are defined, for
> @@ -2492,6 +2498,12 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
>  			return -EINVAL;
>  		error = PAC_RESET_KEYS(me, arg2);
>  		break;
> +	case PR_SET_TAGGED_ADDR_CTRL:
> +		error = SET_TAGGED_ADDR_CTRL(arg2);
> +		break;
> +	case PR_GET_TAGGED_ADDR_CTRL:
> +		error = GET_TAGGED_ADDR_CTRL();
> +		break;
>  	default:
>  		error = -EINVAL;
>  		break;
> -- 
> 2.22.0.410.gd8fdbe21b5-goog
>