Hi Catalin,
...
---------8<---------------- From 7c624777a4e545522dec1b34e60f0229cb2bd59f Mon Sep 17 00:00:00 2001 From: Catalin Marinas catalin.marinas@arm.com Date: Tue, 11 Jun 2019 13:03:38 +0100 Subject: [PATCH] arm64: Introduce prctl() options to control the tagged user addresses ABI
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 | 5 ++- arch/arm64/kernel/process.c | 67 ++++++++++++++++++++++++++++ include/uapi/linux/prctl.h | 5 +++ kernel/sys.c | 16 +++++++ 6 files changed, 99 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 c285d1ce7186..7263d4c973ce 100644 --- a/arch/arm64/include/asm/thread_info.h +++ b/arch/arm64/include/asm/thread_info.h @@ -101,6 +101,7 @@ 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
Can you please put a comment here?
#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 9164ecb5feca..995b9ea11a89 100644 --- a/arch/arm64/include/asm/uaccess.h +++ b/arch/arm64/include/asm/uaccess.h @@ -73,6 +73,9 @@ static inline unsigned long __range_ok(const void __user *addr, unsigned long si { unsigned long ret, limit = current_thread_info()->addr_limit;
- if (test_thread_flag(TIF_TAGGED_ADDR))
addr = untagged_addr(addr);- __chk_user_ptr(addr); asm volatile( // A + B <= C + 1 for all A,B,C, in four easy steps:
@@ -94,7 +97,7 @@ static inline unsigned long __range_ok(const void __user *addr, unsigned long si return ret; } -#define access_ok(addr, size) __range_ok(untagged_addr(addr), size) +#define access_ok(addr, size) __range_ok(addr, size) #define user_addr_max get_fs
#define _ASM_EXTABLE(from, to) \
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);
Nit: in line we the other functions in thread_flush we could have something like "tagged_addr_thread_flush", maybe inlined.
} 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);
process.c seems already a bit "overcrowded". Probably we could move all the tagged_addr features in a separate file. What do you think? It would make easier the implementation of mte as well going forward.
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;
Why do we need two prctl here? We could have only one and use arg2 as set/get and arg3 as a parameter. What do you think?
default: error = -EINVAL; break;