Commit 63f0c603 authored by Catalin Marinas's avatar Catalin Marinas Committed by Will Deacon

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(). 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.
Reviewed-by: default avatarKees Cook <keescook@chromium.org>
Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: default avatarAndrey Konovalov <andreyknvl@google.com>
Signed-off-by: default avatarWill Deacon <will@kernel.org>
parent 2b835e24
......@@ -1110,6 +1110,15 @@ 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
......
......@@ -306,6 +306,14 @@ 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
*
......
......@@ -90,6 +90,7 @@ 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)
......
......@@ -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(
......
......@@ -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>
......@@ -38,6 +39,7 @@
#include <trace/events/power.h>
#include <linux/percpu.h>
#include <linux/thread_info.h>
#include <linux/prctl.h>
#include <asm/alternative.h>
#include <asm/arch_gicv3.h>
......@@ -307,11 +309,18 @@ 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)
......@@ -565,3 +574,67 @@ 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 */
......@@ -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 */
......@@ -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;
......
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