| Message ID | 20170615011203.144108-1-thgarnie@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Wed, Jun 14, 2017 at 6:12 PM, Thomas Garnier <thgarnie@google.com> wrote: > 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 <thgarnie@google.com> Thanks for reworking this series! The bad state correctly BUGs under the LKDTM test: [ 21.171586] lkdtm: Performing direct entry CORRUPT_USER_DS [ 21.172791] lkdtm: setting bad task size limit [ 21.173742] ------------[ cut here ]------------ [ 21.174641] kernel BUG at ./include/linux/syscalls.h:220! ... [ 21.193166] Call Trace: [ 21.193617] ? trace_hardirqs_on_thunk+0x1a/0x1c [ 21.194443] entry_SYSCALL64_slow_path+0x25/0x25 Tested-by: Kees Cook <keescook@chromium.org> -Kees
On Tue, Jun 20, 2017 at 1:24 PM, Kees Cook <keescook@chromium.org> wrote: > On Wed, Jun 14, 2017 at 6:12 PM, Thomas Garnier <thgarnie@google.com> wrote: >> 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 <thgarnie@google.com> > > Thanks for reworking this series! > > The bad state correctly BUGs under the LKDTM test: > > [ 21.171586] lkdtm: Performing direct entry CORRUPT_USER_DS > [ 21.172791] lkdtm: setting bad task size limit > [ 21.173742] ------------[ cut here ]------------ > [ 21.174641] kernel BUG at ./include/linux/syscalls.h:220! > ... > [ 21.193166] Call Trace: > [ 21.193617] ? trace_hardirqs_on_thunk+0x1a/0x1c > [ 21.194443] entry_SYSCALL64_slow_path+0x25/0x25 > > > Tested-by: Kees Cook <keescook@chromium.org> Is everyone happy with this patch for x86? Does this need anything more/different? Thanks! -Kees
On Wed, Jun 28, 2017 at 10:52 AM, Kees Cook <keescook@chromium.org> wrote: > > On Tue, Jun 20, 2017 at 1:24 PM, Kees Cook <keescook@chromium.org> wrote: > > On Wed, Jun 14, 2017 at 6:12 PM, Thomas Garnier <thgarnie@google.com> wrote: > >> 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 <thgarnie@google.com> > > > > Thanks for reworking this series! > > > > The bad state correctly BUGs under the LKDTM test: > > > > [ 21.171586] lkdtm: Performing direct entry CORRUPT_USER_DS > > [ 21.172791] lkdtm: setting bad task size limit > > [ 21.173742] ------------[ cut here ]------------ > > [ 21.174641] kernel BUG at ./include/linux/syscalls.h:220! > > ... > > [ 21.193166] Call Trace: > > [ 21.193617] ? trace_hardirqs_on_thunk+0x1a/0x1c > > [ 21.194443] entry_SYSCALL64_slow_path+0x25/0x25 > > > > > > Tested-by: Kees Cook <keescook@chromium.org> > > Is everyone happy with this patch for x86? Does this need anything > more/different? Asking again. Additional feedback? Anyone wants to pick-it up? > > Thanks! > > -Kees > > -- > Kees Cook > Pixel Security
On Thu, 6 Jul 2017, Thomas Garnier wrote: > On Wed, Jun 28, 2017 at 10:52 AM, Kees Cook <keescook@chromium.org> wrote: > > > > On Tue, Jun 20, 2017 at 1:24 PM, Kees Cook <keescook@chromium.org> wrote: > > > On Wed, Jun 14, 2017 at 6:12 PM, Thomas Garnier <thgarnie@google.com> wrote: > > >> 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 <thgarnie@google.com> > > > > > > Thanks for reworking this series! > > > > > > The bad state correctly BUGs under the LKDTM test: > > > > > > [ 21.171586] lkdtm: Performing direct entry CORRUPT_USER_DS > > > [ 21.172791] lkdtm: setting bad task size limit > > > [ 21.173742] ------------[ cut here ]------------ > > > [ 21.174641] kernel BUG at ./include/linux/syscalls.h:220! > > > ... > > > [ 21.193166] Call Trace: > > > [ 21.193617] ? trace_hardirqs_on_thunk+0x1a/0x1c > > > [ 21.194443] entry_SYSCALL64_slow_path+0x25/0x25 > > > > > > > > > Tested-by: Kees Cook <keescook@chromium.org> > > > > Is everyone happy with this patch for x86? Does this need anything > > more/different? > > Asking again. Additional feedback? Anyone wants to pick-it up? Can do. This needs to be a combo of all 3 I assume as the x86 one contains the function used by all of them, right? Thanks, tglx
On Thu, Jul 6, 2017 at 1:48 PM, Thomas Gleixner <tglx@linutronix.de> wrote: > On Thu, 6 Jul 2017, Thomas Garnier wrote: >> On Wed, Jun 28, 2017 at 10:52 AM, Kees Cook <keescook@chromium.org> wrote: >> > >> > On Tue, Jun 20, 2017 at 1:24 PM, Kees Cook <keescook@chromium.org> wrote: >> > > On Wed, Jun 14, 2017 at 6:12 PM, Thomas Garnier <thgarnie@google.com> wrote: >> > >> 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 <thgarnie@google.com> >> > > >> > > Thanks for reworking this series! >> > > >> > > The bad state correctly BUGs under the LKDTM test: >> > > >> > > [ 21.171586] lkdtm: Performing direct entry CORRUPT_USER_DS >> > > [ 21.172791] lkdtm: setting bad task size limit >> > > [ 21.173742] ------------[ cut here ]------------ >> > > [ 21.174641] kernel BUG at ./include/linux/syscalls.h:220! >> > > ... >> > > [ 21.193166] Call Trace: >> > > [ 21.193617] ? trace_hardirqs_on_thunk+0x1a/0x1c >> > > [ 21.194443] entry_SYSCALL64_slow_path+0x25/0x25 >> > > >> > > >> > > Tested-by: Kees Cook <keescook@chromium.org> >> > >> > Is everyone happy with this patch for x86? Does this need anything >> > more/different? >> >> Asking again. Additional feedback? Anyone wants to pick-it up? > > Can do. This needs to be a combo of all 3 I assume as the x86 one contains > the function used by all of them, right? That is correct. > > Thanks, > > tglx
diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c index cdefcfdd9e63..03505ffbe1b6 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 e00e1bd6e7b3..5161da1a0fa0 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 a059aac9e937..11433f9018e2 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 980c3c9b06f8..ac0cf6fb25d6 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);
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 <thgarnie@google.com> --- v10 redesigns the change to use work flags on set_fs as recommended by Linus and agreed by others. Based on next-20170609 --- 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(-)