[RFC PATCH v2 10/10] powerpc/32: Add stack overflow detection with VMAP stack.

[Christophe Leroy]

To avoid recursive faults, stack overflow detection has to be
performed before writing in the stack in exception prologs.

Do it by checking the alignment. If the stack pointer alignment is
wrong, it means it is pointing to the following or preceding page.

Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxx>
---
 arch/powerpc/kernel/entry_32.S | 12 ++++++++++++
 arch/powerpc/kernel/head_32.h  |  5 ++++-
 arch/powerpc/kernel/head_8xx.S |  3 +++
 3 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index ef296572a513..68e03feb4bd1 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -184,9 +184,11 @@ transfer_to_handler:
          */
 	kuap_save_and_lock r11, r12, r9, r2, r0
 	addi	r2, r12, -THREAD
+#ifndef CONFIG_VMAP_STACK
 	lwz	r9,KSP_LIMIT(r12)
 	cmplw	r1,r9			/* if r1 <= ksp_limit */
 	ble-	stack_ovf		/* then the kernel stack overflowed */
+#endif
 5:
 #if defined(CONFIG_PPC_BOOK3S_32) || defined(CONFIG_E500)
 	lwz	r12,TI_LOCAL_FLAGS(r2)
@@ -298,6 +300,15 @@ reenable_mmu:
  * On kernel stack overflow, load up an initial stack pointer
  * and call StackOverflow(regs), which should not return.
  */
+#ifdef CONFIG_VMAP_STACK
+_GLOBAL(stack_ovf)
+	lis	r11, init_thread_union + THREAD_SIZE - INT_FRAME_SIZE@ha
+	addi	r11, r11, init_thread_union + THREAD_SIZE - INT_FRAME_SIZE@l
+	EXCEPTION_PROLOG_2
+	SAVE_NVGPRS(r11)
+	addi	r3, r1, STACK_FRAME_OVERHEAD
+	EXC_XFER_STD(0, StackOverflow)
+#else
 stack_ovf:
 	/* sometimes we use a statically-allocated stack, which is OK. */
 	lis	r12,_end@h
@@ -319,6 +330,7 @@ stack_ovf:
 	mtspr	SPRN_SRR1,r10
 	SYNC
 	RFI
+#endif
 
 #ifdef CONFIG_TRACE_IRQFLAGS
 trace_syscall_entry_irq_off:
diff --git a/arch/powerpc/kernel/head_32.h b/arch/powerpc/kernel/head_32.h
index 4980babde59e..d442625d9649 100644
--- a/arch/powerpc/kernel/head_32.h
+++ b/arch/powerpc/kernel/head_32.h
@@ -51,7 +51,10 @@
 #endif
 	lwz	r11,TASK_STACK-THREAD(r11)
 	addi	r11, r11, THREAD_SIZE - INT_FRAME_SIZE
-#ifndef CONFIG_VMAP_STACK
+#ifdef CONFIG_VMAP_STACK
+	mtcrf	0xfe, r11
+	bt	32 - THREAD_ALIGN_SHIFT, stack_ovf_trampoline
+#else
 	tophys(r11,r11)
 #endif
 1:
diff --git a/arch/powerpc/kernel/head_8xx.S b/arch/powerpc/kernel/head_8xx.S
index dfd68b72688e..b9c9cfd72b19 100644
--- a/arch/powerpc/kernel/head_8xx.S
+++ b/arch/powerpc/kernel/head_8xx.S
@@ -572,6 +572,9 @@ InstructionBreakpoint:
 	EXCEPTION(0x1e00, Trap_1e, unknown_exception, EXC_XFER_STD)
 	EXCEPTION(0x1f00, Trap_1f, unknown_exception, EXC_XFER_STD)
 
+stack_ovf_trampoline:
+	b	stack_ovf
+
 	. = 0x2000
 
 /* This is the procedure to calculate the data EA for buggy dcbx,dcbi instructions
-- 
2.13.3