Re: [PATCH v16 02/16] arm64: untag user pointers in access_ok and __uaccess_mask_ptr

On Tue, Jun 11, 2019 at 4:57 PM Catalin Marinas catalin.marinas@arm.com wrote:

On Mon, Jun 10, 2019 at 06:53:27PM +0100, Catalin Marinas wrote:

...

On Mon, Jun 03, 2019 at 06:55:04PM +0200, Andrey Konovalov wrote:

...

diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h index e5d5f31c6d36..9164ecb5feca 100644 --- a/arch/arm64/include/asm/uaccess.h +++ b/arch/arm64/include/asm/uaccess.h @@ -94,7 +94,7 @@ static inline unsigned long __range_ok(const void __user *addr, unsigned long si return ret; }

-#define access_ok(addr, size) __range_ok(addr, size) +#define access_ok(addr, size) __range_ok(untagged_addr(addr), size)

I'm going to propose an opt-in method here (RFC for now). We can't have a check in untagged_addr() since this is already used throughout the kernel for both user and kernel addresses (khwasan) but we can add one in __range_ok(). The same prctl() option will be used for controlling the precise/imprecise mode of MTE later on. We can use a TIF_ flag here assuming that this will be called early on and any cloned thread will inherit this.

Updated patch, inlining it below. Once we agreed on the approach, I think Andrey can insert in in this series, probably after patch 2. The differences from the one I posted yesterday:

• renamed PR_* macros together with get/set variants and the possibility to disable the relaxed ABI

• sysctl option - /proc/sys/abi/tagged_addr to disable the ABI globally (just the prctl() opt-in, tasks already using it won't be affected)

And, of course, it needs more testing.

Sure, I'll add it to the series.

Should I drop access_ok() change from my patch, since yours just reverts it?

Thanks!

---------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

#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);
  

}

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;