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authorHeiko Carstens <heiko.carstens@de.ibm.com>2017-02-17 10:13:28 +0300
committerMartin Schwidefsky <schwidefsky@de.ibm.com>2017-02-23 12:06:38 +0300
commitb5a882fcf146c87cb6b67c6df353e1c042b8773d (patch)
treea5c7d041f74567d24d44c17a1f80e86302d738d5
parent606aa4aa0b2c6d7c4f5d2e459922675ea1d7e459 (diff)
downloadlinux-b5a882fcf146c87cb6b67c6df353e1c042b8773d.tar.xz
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>
-rw-r--r--arch/s390/include/asm/processor.h12
-rw-r--r--arch/s390/include/asm/uaccess.h23
-rw-r--r--arch/s390/kernel/entry.S29
-rw-r--r--arch/s390/kernel/entry.h1
-rw-r--r--arch/s390/kernel/process.c13
5 files changed, 53 insertions, 25 deletions
diff --git a/arch/s390/include/asm/processor.h b/arch/s390/include/asm/processor.h
index 3c8fae02ac2d..c57c5c2f2484 100644
--- a/arch/s390/include/asm/processor.h
+++ b/arch/s390/include/asm/processor.h
@@ -15,13 +15,15 @@
#define CIF_MCCK_PENDING 0 /* machine check handling is pending */
#define CIF_ASCE_PRIMARY 1 /* primary asce needs fixup / uaccess */
-#define CIF_NOHZ_DELAY 2 /* delay HZ disable for a tick */
-#define CIF_FPU 3 /* restore FPU registers */
-#define CIF_IGNORE_IRQ 4 /* ignore interrupt (for udelay) */
-#define CIF_ENABLED_WAIT 5 /* in enabled wait state */
+#define CIF_ASCE_SECONDARY 2 /* secondary asce needs fixup / uaccess */
+#define CIF_NOHZ_DELAY 3 /* delay HZ disable for a tick */
+#define CIF_FPU 4 /* restore FPU registers */
+#define CIF_IGNORE_IRQ 5 /* ignore interrupt (for udelay) */
+#define CIF_ENABLED_WAIT 6 /* in enabled wait state */
#define _CIF_MCCK_PENDING _BITUL(CIF_MCCK_PENDING)
#define _CIF_ASCE_PRIMARY _BITUL(CIF_ASCE_PRIMARY)
+#define _CIF_ASCE_SECONDARY _BITUL(CIF_ASCE_SECONDARY)
#define _CIF_NOHZ_DELAY _BITUL(CIF_NOHZ_DELAY)
#define _CIF_FPU _BITUL(CIF_FPU)
#define _CIF_IGNORE_IRQ _BITUL(CIF_IGNORE_IRQ)
@@ -200,10 +202,12 @@ struct stack_frame {
struct task_struct;
struct mm_struct;
struct seq_file;
+struct pt_regs;
typedef int (*dump_trace_func_t)(void *data, unsigned long address, int reliable);
void dump_trace(dump_trace_func_t func, void *data,
struct task_struct *task, unsigned long sp);
+void show_registers(struct pt_regs *regs);
void show_cacheinfo(struct seq_file *m);
diff --git a/arch/s390/include/asm/uaccess.h b/arch/s390/include/asm/uaccess.h
index b2988fc60f65..136932ff4250 100644
--- a/arch/s390/include/asm/uaccess.h
+++ b/arch/s390/include/asm/uaccess.h
@@ -14,6 +14,7 @@
*/
#include <linux/sched.h>
#include <linux/errno.h>
+#include <asm/processor.h>
#include <asm/ctl_reg.h>
#define VERIFY_READ 0
@@ -36,18 +37,20 @@
#define get_ds() (KERNEL_DS)
#define get_fs() (current->thread.mm_segment)
-
-#define set_fs(x) \
-do { \
- unsigned long __pto; \
- current->thread.mm_segment = (x); \
- __pto = current->thread.mm_segment.ar4 ? \
- S390_lowcore.user_asce : S390_lowcore.kernel_asce; \
- __ctl_load(__pto, 7, 7); \
-} while (0)
-
#define segment_eq(a,b) ((a).ar4 == (b).ar4)
+static inline void set_fs(mm_segment_t fs)
+{
+ current->thread.mm_segment = fs;
+ if (segment_eq(fs, KERNEL_DS)) {
+ set_cpu_flag(CIF_ASCE_SECONDARY);
+ __ctl_load(S390_lowcore.kernel_asce, 7, 7);
+ } else {
+ clear_cpu_flag(CIF_ASCE_SECONDARY);
+ __ctl_load(S390_lowcore.user_asce, 7, 7);
+ }
+}
+
static inline int __range_ok(unsigned long addr, unsigned long size)
{
return 1;
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.
diff --git a/arch/s390/kernel/entry.h b/arch/s390/kernel/entry.h
index e79f030dd276..33f901865326 100644
--- a/arch/s390/kernel/entry.h
+++ b/arch/s390/kernel/entry.h
@@ -80,5 +80,6 @@ long sys_s390_pci_mmio_read(unsigned long, void __user *, size_t);
DECLARE_PER_CPU(u64, mt_cycles[8]);
void verify_facilities(void);
+void set_fs_fixup(void);
#endif /* _ENTRY_H */
diff --git a/arch/s390/kernel/process.c b/arch/s390/kernel/process.c
index c5b86b4a1a8b..a49dc2bdeb17 100644
--- a/arch/s390/kernel/process.c
+++ b/arch/s390/kernel/process.c
@@ -234,3 +234,16 @@ unsigned long arch_randomize_brk(struct mm_struct *mm)
ret = PAGE_ALIGN(mm->brk + brk_rnd());
return (ret > mm->brk) ? ret : mm->brk;
}
+
+void set_fs_fixup(void)
+{
+ struct pt_regs *regs = current_pt_regs();
+ static bool warned;
+
+ set_fs(USER_DS);
+ if (warned)
+ return;
+ WARN(1, "Unbalanced set_fs - int code: 0x%x\n", regs->int_code);
+ show_registers(regs);
+ warned = true;
+}