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| author | Heiko Carstens <heiko.carstens@de.ibm.com> | 2017-02-17 08:13:28 +0100 |
|---|---|---|
| committer | Martin Schwidefsky <schwidefsky@de.ibm.com> | 2017-02-23 10:06:38 +0100 |
| commit | b5a882fcf146c87cb6b67c6df353e1c042b8773d (patch) | |
| tree | a5c7d041f74567d24d44c17a1f80e86302d738d5 /arch/s390/kernel/entry.S | |
| parent | 606aa4aa0b2c6d7c4f5d2e459922675ea1d7e459 (diff) | |
| download | lwn-b5a882fcf146c87cb6b67c6df353e1c042b8773d.tar.gz lwn-b5a882fcf146c87cb6b67c6df353e1c042b8773d.zip | |
s390: restore address space when returning to user space
Unbalanced set_fs usages (e.g. early exit from a function and a
forgotten set_fs(USER_DS) call) may lead to a situation where the
secondary asce is the kernel space asce when returning to user
space. This would allow user space to modify kernel space at will.
This would only be possible with the above mentioned kernel bug,
however we can detect this and fix the secondary asce before returning
to user space.
Therefore a new TIF_ASCE_SECONDARY which is used within set_fs. When
returning to user space check if TIF_ASCE_SECONDARY is set, which
would indicate a bug. If it is set print a message to the console,
fixup the secondary asce, and then return to user space.
This is similar to what is being discussed for x86 and arm:
"[RFC] syscalls: Restore address limit after a syscall".
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Diffstat (limited to 'arch/s390/kernel/entry.S')
| -rw-r--r-- | arch/s390/kernel/entry.S | 29 |
1 files changed, 18 insertions, 11 deletions
diff --git a/arch/s390/kernel/entry.S b/arch/s390/kernel/entry.S index ae7d1a230abf..dff2152350a7 100644 --- a/arch/s390/kernel/entry.S +++ b/arch/s390/kernel/entry.S @@ -50,7 +50,8 @@ _TIF_WORK = (_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_NEED_RESCHED | \ _TIF_UPROBE) _TIF_TRACE = (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | _TIF_SECCOMP | \ _TIF_SYSCALL_TRACEPOINT) -_CIF_WORK = (_CIF_MCCK_PENDING | _CIF_ASCE_PRIMARY | _CIF_FPU) +_CIF_WORK = (_CIF_MCCK_PENDING | _CIF_ASCE_PRIMARY | \ + _CIF_ASCE_SECONDARY | _CIF_FPU) _PIF_WORK = (_PIF_PER_TRAP) #define BASED(name) name-cleanup_critical(%r13) @@ -339,8 +340,8 @@ ENTRY(system_call) jo .Lsysc_notify_resume TSTMSK __LC_CPU_FLAGS,_CIF_FPU jo .Lsysc_vxrs - TSTMSK __LC_CPU_FLAGS,_CIF_ASCE_PRIMARY - jo .Lsysc_asce_primary + TSTMSK __LC_CPU_FLAGS,(_CIF_ASCE_PRIMARY|_CIF_ASCE_SECONDARY) + jnz .Lsysc_asce j .Lsysc_return # beware of critical section cleanup # @@ -358,12 +359,15 @@ ENTRY(system_call) jg s390_handle_mcck # TIF bit will be cleared by handler # -# _CIF_ASCE_PRIMARY is set, load user space asce +# _CIF_ASCE_PRIMARY and/or CIF_ASCE_SECONDARY set, load user space asce # -.Lsysc_asce_primary: +.Lsysc_asce: ni __LC_CPU_FLAGS+7,255-_CIF_ASCE_PRIMARY lctlg %c1,%c1,__LC_USER_ASCE # load primary asce - j .Lsysc_return + TSTMSK __LC_CPU_FLAGS,_CIF_ASCE_SECONDARY + jz .Lsysc_return + larl %r14,.Lsysc_return + jg set_fs_fixup # # CIF_FPU is set, restore floating-point controls and floating-point registers. @@ -661,8 +665,8 @@ ENTRY(io_int_handler) jo .Lio_notify_resume TSTMSK __LC_CPU_FLAGS,_CIF_FPU jo .Lio_vxrs - TSTMSK __LC_CPU_FLAGS,_CIF_ASCE_PRIMARY - jo .Lio_asce_primary + TSTMSK __LC_CPU_FLAGS,(_CIF_ASCE_PRIMARY|_CIF_ASCE_SECONDARY) + jnz .Lio_asce j .Lio_return # beware of critical section cleanup # @@ -675,12 +679,15 @@ ENTRY(io_int_handler) j .Lio_return # -# _CIF_ASCE_PRIMARY is set, load user space asce +# _CIF_ASCE_PRIMARY and/or CIF_ASCE_SECONDARY set, load user space asce # -.Lio_asce_primary: +.Lio_asce: ni __LC_CPU_FLAGS+7,255-_CIF_ASCE_PRIMARY lctlg %c1,%c1,__LC_USER_ASCE # load primary asce - j .Lio_return + TSTMSK __LC_CPU_FLAGS,_CIF_ASCE_SECONDARY + jz .Lio_return + larl %r14,.Lio_return + jg set_fs_fixup # # CIF_FPU is set, restore floating-point controls and floating-point registers. |