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().
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 --- arch/arm64/include/asm/processor.h | 6 +++ arch/arm64/include/asm/thread_info.h | 1 + arch/arm64/include/asm/uaccess.h | 3 +- arch/arm64/kernel/process.c | 67 ++++++++++++++++++++++++++++ include/uapi/linux/prctl.h | 5 +++ kernel/sys.c | 16 +++++++ 6 files changed, 97 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h index fcd0e691b1ea..fee457456aa8 100644 --- a/arch/arm64/include/asm/processor.h +++ b/arch/arm64/include/asm/processor.h @@ -307,6 +307,12 @@ extern void __init minsigstksz_setup(void); /* PR_PAC_RESET_KEYS prctl */ #define PAC_RESET_KEYS(tsk, arg) ptrauth_prctl_reset_keys(tsk, arg)
+/* PR_TAGGED_ADDR 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() + /* * For CONFIG_GCC_PLUGIN_STACKLEAK * diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h index f1d032be628a..354a31d2b737 100644 --- a/arch/arm64/include/asm/thread_info.h +++ b/arch/arm64/include/asm/thread_info.h @@ -99,6 +99,7 @@ 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 df729afca0ba..995b9ea11a89 100644 --- a/arch/arm64/include/asm/uaccess.h +++ b/arch/arm64/include/asm/uaccess.h @@ -73,7 +73,8 @@ 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 (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 3767fb21a5b8..69d0be1fc708 100644 --- a/arch/arm64/kernel/process.c +++ b/arch/arm64/kernel/process.c @@ -30,6 +30,7 @@ #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> @@ -323,6 +324,7 @@ void flush_thread(void) fpsimd_flush_thread(); tls_thread_flush(); flush_ptrace_hw_breakpoint(current); + clear_thread_flag(TIF_TAGGED_ADDR); }
void release_thread(struct task_struct *dead_task) @@ -552,3 +554,68 @@ void arch_setup_new_exec(void)
ptrauth_thread_init_user(current); } + +/* + * 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; + + if (arg & PR_TAGGED_ADDR_ENABLE) + set_thread_flag(TIF_TAGGED_ADDR); + else + clear_thread_flag(TIF_TAGGED_ADDR); + + 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); 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..ec48396b4943 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 +2498,16 @@ 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: + if (arg3 || arg4 || arg5) + return -EINVAL; + error = SET_TAGGED_ADDR_CTRL(arg2); + break; + case PR_GET_TAGGED_ADDR_CTRL: + if (arg2 || arg3 || arg4 || arg5) + return -EINVAL; + error = GET_TAGGED_ADDR_CTRL(); + break; default: error = -EINVAL; break;