Commit-ID: 5ea0727b163cb5575e36397a12eade68a1f35f24 Gitweb: http://git.kernel.org/tip/5ea0727b163cb5575e36397a12eade68a1f35f24 Author: Thomas Garnier <[email protected]> AuthorDate: Wed, 14 Jun 2017 18:12:01 -0700 Committer: Thomas Gleixner <[email protected]> CommitDate: Sat, 8 Jul 2017 14:05:32 +0200
x86/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 addr_limit_user_check function is added as a cross-architecture function to check the address limit. [1] https://bugs.chromium.org/p/project-zero/issues/detail?id=990 Signed-off-by: Thomas Garnier <[email protected]> Signed-off-by: Thomas Gleixner <[email protected]> Cc: Mark Rutland <[email protected]> Cc: [email protected] Cc: Catalin Marinas <[email protected]> Cc: Will Deacon <[email protected]> Cc: David Howells <[email protected]> Cc: Dave Hansen <[email protected]> Cc: Miroslav Benes <[email protected]> Cc: Chris Metcalf <[email protected]> Cc: Pratyush Anand <[email protected]> Cc: Russell King <[email protected]> Cc: Petr Mladek <[email protected]> Cc: Rik van Riel <[email protected]> Cc: Kees Cook <[email protected]> Cc: Arnd Bergmann <[email protected]> Cc: Al Viro <[email protected]> Cc: Andy Lutomirski <[email protected]> Cc: Josh Poimboeuf <[email protected]> Cc: [email protected] Cc: Will Drewry <[email protected]> Cc: [email protected] Cc: Oleg Nesterov <[email protected]> Cc: Andy Lutomirski <[email protected]> Cc: Paolo Bonzini <[email protected]> Link: http://lkml.kernel.org/r/[email protected] --- arch/x86/entry/common.c | 3 +++ arch/x86/include/asm/thread_info.h | 5 ++++- arch/x86/include/asm/uaccess.h | 7 ++++++- include/linux/syscalls.h | 16 ++++++++++++++++ 4 files changed, 29 insertions(+), 2 deletions(-) diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c index cdefcfd..03505ff 100644 --- a/arch/x86/entry/common.c +++ b/arch/x86/entry/common.c @@ -23,6 +23,7 @@ #include <linux/user-return-notifier.h> #include <linux/uprobes.h> #include <linux/livepatch.h> +#include <linux/syscalls.h> #include <asm/desc.h> #include <asm/traps.h> @@ -183,6 +184,8 @@ __visible inline void prepare_exit_to_usermode(struct pt_regs *regs) struct thread_info *ti = current_thread_info(); u32 cached_flags; + addr_limit_user_check(); + if (IS_ENABLED(CONFIG_PROVE_LOCKING) && WARN_ON(!irqs_disabled())) local_irq_disable(); diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h index e00e1bd..5161da1a 100644 --- a/arch/x86/include/asm/thread_info.h +++ b/arch/x86/include/asm/thread_info.h @@ -98,6 +98,7 @@ struct thread_info { #define TIF_SYSCALL_TRACEPOINT 28 /* syscall tracepoint instrumentation */ #define TIF_ADDR32 29 /* 32-bit address space on 64 bits */ #define TIF_X32 30 /* 32-bit native x86-64 binary */ +#define TIF_FSCHECK 31 /* Check FS is USER_DS on return */ #define _TIF_SYSCALL_TRACE (1 << TIF_SYSCALL_TRACE) #define _TIF_NOTIFY_RESUME (1 << TIF_NOTIFY_RESUME) @@ -122,6 +123,7 @@ struct thread_info { #define _TIF_SYSCALL_TRACEPOINT (1 << TIF_SYSCALL_TRACEPOINT) #define _TIF_ADDR32 (1 << TIF_ADDR32) #define _TIF_X32 (1 << TIF_X32) +#define _TIF_FSCHECK (1 << TIF_FSCHECK) /* * work to do in syscall_trace_enter(). Also includes TIF_NOHZ for @@ -137,7 +139,8 @@ struct thread_info { (_TIF_SYSCALL_TRACE | _TIF_NOTIFY_RESUME | _TIF_SIGPENDING | \ _TIF_NEED_RESCHED | _TIF_SINGLESTEP | _TIF_SYSCALL_EMU | \ _TIF_SYSCALL_AUDIT | _TIF_USER_RETURN_NOTIFY | _TIF_UPROBE | \ - _TIF_PATCH_PENDING | _TIF_NOHZ | _TIF_SYSCALL_TRACEPOINT) + _TIF_PATCH_PENDING | _TIF_NOHZ | _TIF_SYSCALL_TRACEPOINT | \ + _TIF_FSCHECK) /* flags to check in __switch_to() */ #define _TIF_WORK_CTXSW \ diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h index a059aac..11433f9 100644 --- a/arch/x86/include/asm/uaccess.h +++ b/arch/x86/include/asm/uaccess.h @@ -26,7 +26,12 @@ #define get_ds() (KERNEL_DS) #define get_fs() (current->thread.addr_limit) -#define set_fs(x) (current->thread.addr_limit = (x)) +static inline void set_fs(mm_segment_t fs) +{ + current->thread.addr_limit = fs; + /* On user-mode return, check fs is correct */ + set_thread_flag(TIF_FSCHECK); +} #define segment_eq(a, b) ((a).seg == (b).seg) diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h index 980c3c9..ac0cf6f 100644 --- a/include/linux/syscalls.h +++ b/include/linux/syscalls.h @@ -206,6 +206,22 @@ extern struct trace_event_functions exit_syscall_print_funcs; } \ static inline long SYSC##name(__MAP(x,__SC_DECL,__VA_ARGS__)) +#ifdef TIF_FSCHECK +/* + * Called before coming back to user-mode. Returning to user-mode with an + * address limit different than USER_DS can allow to overwrite kernel memory. + */ +static inline void addr_limit_user_check(void) +{ + + if (!test_thread_flag(TIF_FSCHECK)) + return; + + BUG_ON(!segment_eq(get_fs(), USER_DS)); + clear_thread_flag(TIF_FSCHECK); +} +#endif + asmlinkage long sys32_quotactl(unsigned int cmd, const char __user *special, qid_t id, void __user *addr); asmlinkage long sys_time(time_t __user *tloc);
