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authorCatalin Marinas <catalin.marinas@arm.com>2019-07-23 19:58:39 +0200
committerWill Deacon <will@kernel.org>2019-08-06 18:08:45 +0100
commit63f0c60379650d82250f22e4cf4137ef3dc4f43d (patch)
treeaf76cdc5d0eeca023d86c43664d073af25d63546 /arch
parent2b835e24b5c6f9c633ff51973581ee7ca7b3e8ec (diff)
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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: Kees Cook <keescook@chromium.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> Signed-off-by: Andrey Konovalov <andreyknvl@google.com> Signed-off-by: Will Deacon <will@kernel.org>
Diffstat (limited to 'arch')
-rw-r--r--arch/arm64/Kconfig9
-rw-r--r--arch/arm64/include/asm/processor.h8
-rw-r--r--arch/arm64/include/asm/thread_info.h1
-rw-r--r--arch/arm64/include/asm/uaccess.h4
-rw-r--r--arch/arm64/kernel/process.c73
5 files changed, 94 insertions, 1 deletions
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 3adcec05b1f6..5d254178b9ca 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -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
diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
index 844e2964b0f5..28eed40ffc12 100644
--- a/arch/arm64/include/asm/processor.h
+++ b/arch/arm64/include/asm/processor.h
@@ -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
*
diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h
index 180b34ec5965..012238d8e58d 100644
--- a/arch/arm64/include/asm/thread_info.h
+++ b/arch/arm64/include/asm/thread_info.h
@@ -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)
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 f674f28df663..76b7c55026aa 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>
@@ -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 */