ARM: save and reset the address limit when entering an exception

When we enter an exception, the current address limit should not apply
to the exception context: if the exception context wishes to access
kernel space via the user accessors (eg, perf code), it must explicitly
request such access.

Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

5 files changed, 20 insertions, 6 deletions

diff --git a/arch/arm/include/asm/ptrace.h b/arch/arm/include/asm/ptrace.h
index 0ef0093800f2..e9c9a117bd25 100644
--- a/arch/arm/include/asm/ptrace.h
+++ b/arch/arm/include/asm/ptrace.h
@@ -22,7 +22,7 @@ struct pt_regs {
 struct svc_pt_regs {
         struct pt_regs regs;
         u32 dacr;
-        u32 unused;
+        u32 addr_limit;
 };
 
 #define to_svc_pt_regs(r) container_of(r, struct svc_pt_regs, regs)
diff --git a/arch/arm/kernel/asm-offsets.c b/arch/arm/kernel/asm-offsets.c
index 9a8ce342cd82..608008229c7d 100644
--- a/arch/arm/kernel/asm-offsets.c
+++ b/arch/arm/kernel/asm-offsets.c
@@ -109,6 +109,7 @@ int main(void)
   DEFINE(S_OLD_R0,              offsetof(struct pt_regs, ARM_ORIG_r0));
   DEFINE(PT_REGS_SIZE,          sizeof(struct pt_regs));
   DEFINE(SVC_DACR,              offsetof(struct svc_pt_regs, dacr));
+  DEFINE(SVC_ADDR_LIMIT,        offsetof(struct svc_pt_regs, addr_limit));
   DEFINE(SVC_REGS_SIZE,         sizeof(struct svc_pt_regs));
   BLANK();
 #ifdef CONFIG_CACHE_L2X0
diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index 0d6f5413be18..bc5f50799d75 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -185,6 +185,12 @@ ENDPROC(__und_invalid)
         @
         stmia   r7, {r2 - r6}
 
+        get_thread_info tsk
+        ldr     r0, [tsk, #TI_ADDR_LIMIT]
+        mov     r1, #TASK_SIZE
+        str     r1, [tsk, #TI_ADDR_LIMIT]
+        str     r0, [sp, #SVC_ADDR_LIMIT]
+
         uaccess_save r0
         .if \uaccess
         uaccess_disable r0
@@ -213,7 +219,6 @@ __irq_svc:
         irq_handler
 
 #ifdef CONFIG_PREEMPT
-        get_thread_info tsk
         ldr     r8, [tsk, #TI_PREEMPT]          @ get preempt count
         ldr     r0, [tsk, #TI_FLAGS]            @ get flags
         teq     r8, #0                          @ if preempt count != 0
diff --git a/arch/arm/kernel/entry-header.S b/arch/arm/kernel/entry-header.S
index 5e1d029147cb..6391728c8f03 100644
--- a/arch/arm/kernel/entry-header.S
+++ b/arch/arm/kernel/entry-header.S
@@ -215,7 +215,9 @@
         blne    trace_hardirqs_off
 #endif
         .endif
+        ldr     r1, [sp, #SVC_ADDR_LIMIT]
         uaccess_restore
+        str     r1, [tsk, #TI_ADDR_LIMIT]
 
 #ifndef CONFIG_THUMB2_KERNEL
         @ ARM mode SVC restore
@@ -259,7 +261,9 @@
         @ on the stack remains correct).
         @
         .macro  svc_exit_via_fiq
+        ldr     r1, [sp, #SVC_ADDR_LIMIT]
         uaccess_restore
+        str     r1, [tsk, #TI_ADDR_LIMIT]
 #ifndef CONFIG_THUMB2_KERNEL
         @ ARM mode restore
         mov     r0, sp
diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index f1c720c0d568..612eb530f33f 100644
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -96,19 +96,23 @@ void __show_regs(struct pt_regs *regs)
         unsigned long flags;
         char buf[64];
 #ifndef CONFIG_CPU_V7M
-        unsigned int domain;
+        unsigned int domain, fs;
 #ifdef CONFIG_CPU_SW_DOMAIN_PAN
         /*
          * Get the domain register for the parent context. In user
          * mode, we don't save the DACR, so lets use what it should
          * be. For other modes, we place it after the pt_regs struct.
          */
-        if (user_mode(regs))
+        if (user_mode(regs)) {
                 domain = DACR_UACCESS_ENABLE;
-        else
+                fs = get_fs();
+        } else {
                 domain = to_svc_pt_regs(regs)->dacr;
+                fs = to_svc_pt_regs(regs)->addr_limit;
+        }
 #else
         domain = get_domain();
+        fs = get_fs();
 #endif
 #endif
 
@@ -144,7 +148,7 @@ void __show_regs(struct pt_regs *regs)
                 if ((domain & domain_mask(DOMAIN_USER)) ==
                     domain_val(DOMAIN_USER, DOMAIN_NOACCESS))
                         segment = "none";
-                else if (get_fs() == get_ds())
+                else if (fs == get_ds())
                         segment = "kernel";
                 else
                         segment = "user";