sh: Provide diagnostic kernel stack checks

Enable kernel stack checking code in both the dynamic ftrace and mcount
code paths. Check the stack to see if it's overflowing and make sure
that the stack pointer contains an address that's either in init_stack
or after the bss.

Signed-off-by: Matt Fleming <matt@console-pimps.org>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

3 files changed, 97 insertions, 0 deletions

diff --git a/arch/sh/Kconfig.debug b/arch/sh/Kconfig.debug
index 39224b57c6ef..52a132c24aab 100644
--- a/arch/sh/Kconfig.debug
+++ b/arch/sh/Kconfig.debug
@@ -123,4 +123,15 @@ config SH64_SR_WATCH
         bool "Debug: set SR.WATCH to enable hardware watchpoints and trace"
         depends on SUPERH64
 
+config STACK_DEBUG
+        bool "Enable diagnostic checks of the kernel stack"
+        depends on FUNCTION_TRACER
+        select DEBUG_STACKOVERFLOW
+        default n
+        help
+          This option allows checks to be performed on the kernel stack
+          at runtime. Saying Y here will add overhead to every function
+          call and will therefore incur a major performance hit. Most
+          users should say N.
+
 endmenu
diff --git a/arch/sh/kernel/asm-offsets.c b/arch/sh/kernel/asm-offsets.c
index 99aceb28ee24..d218e808294e 100644
--- a/arch/sh/kernel/asm-offsets.c
+++ b/arch/sh/kernel/asm-offsets.c
@@ -26,6 +26,7 @@ int main(void)
         DEFINE(TI_CPU,          offsetof(struct thread_info, cpu));
         DEFINE(TI_PRE_COUNT,    offsetof(struct thread_info, preempt_count));
         DEFINE(TI_RESTART_BLOCK,offsetof(struct thread_info, restart_block));
+        DEFINE(TI_SIZE,         sizeof(struct thread_info));
 
 #ifdef CONFIG_HIBERNATION
         DEFINE(PBE_ADDRESS, offsetof(struct pbe, address));
diff --git a/arch/sh/lib/mcount.S b/arch/sh/lib/mcount.S
index 71e87f9b4fda..8596483f7b41 100644
--- a/arch/sh/lib/mcount.S
+++ b/arch/sh/lib/mcount.S
@@ -9,6 +9,8 @@
  * for more details.
  */
 #include <asm/ftrace.h>
+#include <asm/thread_info.h>
+#include <asm/asm-offsets.h>
 
 #define MCOUNT_ENTER()          \
         mov.l   r4, @-r15;      \
@@ -28,6 +30,55 @@
         rts;                    \
          mov.l  @r15+, r4
 
+#ifdef CONFIG_STACK_DEBUG
+/*
+ * Perform diagnostic checks on the state of the kernel stack.
+ *
+ * Check for stack overflow. If there is less than 1KB free
+ * then it has overflowed.
+ *
+ * Make sure the stack pointer contains a valid address. Valid
+ * addresses for kernel stacks are anywhere after the bss
+ * (after _ebss) and anywhere in init_thread_union (init_stack).
+ */
+#define STACK_CHECK()                                   \
+        mov     #(THREAD_SIZE >> 10), r0;               \
+        shll8   r0;                                     \
+        shll2   r0;                                     \
+                                                        \
+        /* r1 = sp & (THREAD_SIZE - 1) */               \
+        mov     #-1, r1;                                \
+        add     r0, r1;                                 \
+        and     r15, r1;                                \
+                                                        \
+        mov     #TI_SIZE, r3;                           \
+        mov     #(STACK_WARN >> 8), r2;                 \
+        shll8   r2;                                     \
+        add     r3, r2;                                 \
+                                                        \
+        /* Is the stack overflowing? */                 \
+        cmp/hi  r2, r1;                                 \
+        bf      stack_panic;                            \
+                                                        \
+        /* If sp > _ebss then we're OK. */              \
+        mov.l   .L_ebss, r1;                            \
+        cmp/hi  r1, r15;                                \
+        bt      1f;                                     \
+                                                        \
+        /* If sp < init_stack, we're not OK. */         \
+        mov.l   .L_init_thread_union, r1;               \
+        cmp/hs  r1, r15;                                \
+        bf      stack_panic;                            \
+                                                        \
+        /* If sp > init_stack && sp < _ebss, not OK. */ \
+        add     r0, r1;                                 \
+        cmp/hs  r1, r15;                                \
+        bt      stack_panic;                            \
+1:
+#else
+#define STACK_CHECK()
+#endif /* CONFIG_STACK_DEBUG */
+
         .align 2
         .globl  _mcount
         .type   _mcount,@function
@@ -41,6 +92,8 @@ mcount:
         tst     r0, r0
         bf      ftrace_stub
 #endif
+        STACK_CHECK()
+
         MCOUNT_ENTER()
 
 #ifdef CONFIG_DYNAMIC_FTRACE
@@ -73,6 +126,8 @@ ftrace_caller:
         tst     r0, r0
         bf      ftrace_stub
 
+        STACK_CHECK()
+
         MCOUNT_ENTER()
 
         .globl ftrace_call
@@ -100,6 +155,36 @@ ftrace_stub:
         rts
          nop
 
+#ifdef CONFIG_STACK_DEBUG
+        .globl  stack_panic
+stack_panic:
+        mov.l   .Ldump_stack, r0
+        jsr     @r0
+         nop
+
+        mov.l   .Lpanic, r0
+        jsr     @r0
+         mov.l  .Lpanic_s, r4
+
+        rts
+         nop
+
         .align 2
 .Lfunction_trace_stop:
         .long   function_trace_stop
+.L_ebss:
+        .long   _ebss
+.L_init_thread_union:
+        .long   init_thread_union
+.Lpanic:
+        .long   panic
+.Lpanic_s:
+        .long   .Lpanic_str
+.Ldump_stack:
+        .long   dump_stack
+
+        .section        .rodata
+        .align 2
+.Lpanic_str:
+        .string "Stack error"
+#endif /* CONFIG_STACK_DEBUG */