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arm/syscalls: Check address limit on user-mode return
Ensure the address limit is a user-mode segment before returning to user-mode. Otherwise a process can corrupt kernel-mode memory and elevate privileges [1]. The set_fs function sets the TIF_SETFS flag to force a slow path on return. In the slow path, the address limit is checked to be USER_DS if needed. The TIF_SETFS flag is added to _TIF_WORK_MASK shifting _TIF_SYSCALL_WORK for arm instruction immediate support. The global work mask is too big to used on a single instruction so adapt ret_fast_syscall. [1] https://bugs.chromium.org/p/project-zero/issues/detail?id=990 Signed-off-by: Thomas Garnier <thgarnie@google.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Mark Rutland <mark.rutland@arm.com> Cc: kernel-hardening@lists.openwall.com Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will.deacon@arm.com> Cc: David Howells <dhowells@redhat.com> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Miroslav Benes <mbenes@suse.cz> Cc: Chris Metcalf <cmetcalf@mellanox.com> Cc: Pratyush Anand <panand@redhat.com> Cc: Russell King <linux@armlinux.org.uk> Cc: Petr Mladek <pmladek@suse.com> Cc: Rik van Riel <riel@redhat.com> Cc: Kees Cook <keescook@chromium.org> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Andy Lutomirski <luto@kernel.org> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Cc: linux-arm-kernel@lists.infradead.org Cc: Will Drewry <wad@chromium.org> Cc: linux-api@vger.kernel.org Cc: Oleg Nesterov <oleg@redhat.com> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Paolo Bonzini <pbonzini@redhat.com> Link: http://lkml.kernel.org/r/20170615011203.144108-2-thgarnie@google.com
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@ -139,10 +139,11 @@ extern int vfp_restore_user_hwstate(struct user_vfp __user *,
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#define TIF_NEED_RESCHED 1 /* rescheduling necessary */
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#define TIF_NOTIFY_RESUME 2 /* callback before returning to user */
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#define TIF_UPROBE 3 /* breakpointed or singlestepping */
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#define TIF_SYSCALL_TRACE 4 /* syscall trace active */
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#define TIF_SYSCALL_AUDIT 5 /* syscall auditing active */
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#define TIF_SYSCALL_TRACEPOINT 6 /* syscall tracepoint instrumentation */
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#define TIF_SECCOMP 7 /* seccomp syscall filtering active */
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#define TIF_FSCHECK 4 /* Check FS is USER_DS on return */
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#define TIF_SYSCALL_TRACE 5 /* syscall trace active */
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#define TIF_SYSCALL_AUDIT 6 /* syscall auditing active */
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#define TIF_SYSCALL_TRACEPOINT 7 /* syscall tracepoint instrumentation */
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#define TIF_SECCOMP 8 /* seccomp syscall filtering active */
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#define TIF_NOHZ 12 /* in adaptive nohz mode */
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#define TIF_USING_IWMMXT 17
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@ -153,6 +154,7 @@ extern int vfp_restore_user_hwstate(struct user_vfp __user *,
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#define _TIF_NEED_RESCHED (1 << TIF_NEED_RESCHED)
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#define _TIF_NOTIFY_RESUME (1 << TIF_NOTIFY_RESUME)
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#define _TIF_UPROBE (1 << TIF_UPROBE)
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#define _TIF_FSCHECK (1 << TIF_FSCHECK)
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#define _TIF_SYSCALL_TRACE (1 << TIF_SYSCALL_TRACE)
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#define _TIF_SYSCALL_AUDIT (1 << TIF_SYSCALL_AUDIT)
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#define _TIF_SYSCALL_TRACEPOINT (1 << TIF_SYSCALL_TRACEPOINT)
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@ -167,7 +169,8 @@ extern int vfp_restore_user_hwstate(struct user_vfp __user *,
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* Change these and you break ASM code in entry-common.S
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*/
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#define _TIF_WORK_MASK (_TIF_NEED_RESCHED | _TIF_SIGPENDING | \
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_TIF_NOTIFY_RESUME | _TIF_UPROBE)
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_TIF_NOTIFY_RESUME | _TIF_UPROBE | \
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_TIF_FSCHECK)
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#endif /* __KERNEL__ */
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#endif /* __ASM_ARM_THREAD_INFO_H */
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@ -77,6 +77,8 @@ static inline void set_fs(mm_segment_t fs)
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{
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current_thread_info()->addr_limit = fs;
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modify_domain(DOMAIN_KERNEL, fs ? DOMAIN_CLIENT : DOMAIN_MANAGER);
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/* On user-mode return, check fs is correct */
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set_thread_flag(TIF_FSCHECK);
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}
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#define segment_eq(a, b) ((a) == (b))
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@ -41,7 +41,9 @@ ret_fast_syscall:
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UNWIND(.cantunwind )
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disable_irq_notrace @ disable interrupts
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ldr r1, [tsk, #TI_FLAGS] @ re-check for syscall tracing
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tst r1, #_TIF_SYSCALL_WORK | _TIF_WORK_MASK
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tst r1, #_TIF_SYSCALL_WORK
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bne fast_work_pending
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tst r1, #_TIF_WORK_MASK
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bne fast_work_pending
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/* perform architecture specific actions before user return */
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@ -67,12 +69,15 @@ ret_fast_syscall:
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str r0, [sp, #S_R0 + S_OFF]! @ save returned r0
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disable_irq_notrace @ disable interrupts
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ldr r1, [tsk, #TI_FLAGS] @ re-check for syscall tracing
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tst r1, #_TIF_SYSCALL_WORK | _TIF_WORK_MASK
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tst r1, #_TIF_SYSCALL_WORK
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bne fast_work_pending
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tst r1, #_TIF_WORK_MASK
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beq no_work_pending
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UNWIND(.fnend )
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ENDPROC(ret_fast_syscall)
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/* Slower path - fall through to work_pending */
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fast_work_pending:
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#endif
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tst r1, #_TIF_SYSCALL_WORK
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@ -14,6 +14,7 @@
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#include <linux/uaccess.h>
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#include <linux/tracehook.h>
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#include <linux/uprobes.h>
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#include <linux/syscalls.h>
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#include <asm/elf.h>
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#include <asm/cacheflush.h>
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@ -571,6 +572,10 @@ do_work_pending(struct pt_regs *regs, unsigned int thread_flags, int syscall)
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* Update the trace code with the current status.
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*/
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trace_hardirqs_off();
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/* Check valid user FS if needed */
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addr_limit_user_check();
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do {
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if (likely(thread_flags & _TIF_NEED_RESCHED)) {
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schedule();
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