[PATCH] x86/dumpstack/64: Add guard pages to stack_info

[Peter Zijlstra]

On Wed, Sep 15, 2021 at 09:51:57AM +0800, 王贇 wrote:

> > +
> > +	if (in_exception_stack_guard((void *)address))
> > +		pr_emerg("PANIC: exception stack guard: 0x%lx\n", address);
> >  #endif
> >  
> >  	pr_emerg("PANIC: double fault, error_code: 0x%lx\n", error_code);
> > 
> 
> The panic triggered as below after the stack size recovered, I found this info
> could be helpful, maybe we should keep it?

Could you please test this?

---
Subject: x86/dumpstack/64: Add guard pages to stack_info
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date: Wed Sep 15 17:12:59 CEST 2021

Explicitly add the exception stack guard pages to stack_info and
report on them from #DF.

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
 arch/x86/include/asm/cpu_entry_area.h |    3 +++
 arch/x86/include/asm/stacktrace.h     |    3 ++-
 arch/x86/kernel/dumpstack_64.c        |   17 ++++++++++++++++-
 arch/x86/kernel/traps.c               |   17 ++++++++++++++++-
 4 files changed, 37 insertions(+), 3 deletions(-)

--- a/arch/x86/include/asm/cpu_entry_area.h
+++ b/arch/x86/include/asm/cpu_entry_area.h
@@ -61,6 +61,9 @@ enum exception_stack_ordering {
 #define CEA_ESTACK_OFFS(st)					\
 	offsetof(struct cea_exception_stacks, st## _stack)
 
+#define CEA_EGUARD_OFFS(st)					\
+	offsetof(struct cea_exception_stacks, st## _stack_guard)
+
 #define CEA_ESTACK_PAGES					\
 	(sizeof(struct cea_exception_stacks) / PAGE_SIZE)
 
--- a/arch/x86/include/asm/stacktrace.h
+++ b/arch/x86/include/asm/stacktrace.h
@@ -14,13 +14,14 @@
 #include <asm/switch_to.h>
 
 enum stack_type {
-	STACK_TYPE_UNKNOWN,
+	STACK_TYPE_UNKNOWN = 0,
 	STACK_TYPE_TASK,
 	STACK_TYPE_IRQ,
 	STACK_TYPE_SOFTIRQ,
 	STACK_TYPE_ENTRY,
 	STACK_TYPE_EXCEPTION,
 	STACK_TYPE_EXCEPTION_LAST = STACK_TYPE_EXCEPTION + N_EXCEPTION_STACKS-1,
+	STACK_TYPE_GUARD = 0x80,
 };
 
 struct stack_info {
--- a/arch/x86/kernel/dumpstack_64.c
+++ b/arch/x86/kernel/dumpstack_64.c
@@ -32,9 +32,15 @@ const char *stack_type_name(enum stack_t
 {
 	BUILD_BUG_ON(N_EXCEPTION_STACKS != 6);
 
+	if (type == STACK_TYPE_TASK)
+		return "TASK";
+
 	if (type == STACK_TYPE_IRQ)
 		return "IRQ";
 
+	if (type == STACK_TYPE_SOFTIRQ)
+		return "SOFTIRQ";
+
 	if (type == STACK_TYPE_ENTRY) {
 		/*
 		 * On 64-bit, we have a generic entry stack that we
@@ -63,6 +69,11 @@ struct estack_pages {
 };
 
 #define EPAGERANGE(st)							\
+	[PFN_DOWN(CEA_EGUARD_OFFS(st))] = {				\
+		.offs	= CEA_EGUARD_OFFS(st),				\
+		.size	= PAGE_SIZE,					\
+		.type	= STACK_TYPE_GUARD +				\
+			  STACK_TYPE_EXCEPTION + ESTACK_ ##st, },	\
 	[PFN_DOWN(CEA_ESTACK_OFFS(st)) ...				\
 	 PFN_DOWN(CEA_ESTACK_OFFS(st) + CEA_ESTACK_SIZE(st) - 1)] = {	\
 		.offs	= CEA_ESTACK_OFFS(st),				\
@@ -111,10 +122,11 @@ static __always_inline bool in_exception
 	k = (stk - begin) >> PAGE_SHIFT;
 	/* Lookup the page descriptor */
 	ep = &estack_pages[k];
-	/* Guard page? */
+	/* unknown entry */
 	if (!ep->size)
 		return false;
 
+
 	begin += (unsigned long)ep->offs;
 	end = begin + (unsigned long)ep->size;
 	regs = (struct pt_regs *)end - 1;
@@ -193,6 +205,9 @@ int get_stack_info(unsigned long *stack,
 	if (!get_stack_info_noinstr(stack, task, info))
 		goto unknown;
 
+	if (info->type & STACK_TYPE_GUARD)
+		goto unknown;
+
 	/*
 	 * Make sure we don't iterate through any given stack more than once.
 	 * If it comes up a second time then there's something wrong going on:
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -461,6 +461,19 @@ DEFINE_IDTENTRY_DF(exc_double_fault)
 	}
 #endif
 
+#ifdef CONFIG_X86_64
+	{
+		struct stack_info info;
+
+		if (get_stack_info_noinstr((void *)address, current, &info) &&
+		    info.type & STACK_TYPE_GUARD) {
+			const char *name = stack_type_name(info.type & ~STACK_TYPE_GUARD);
+			pr_emerg("BUG: %s stack guard hit at %p (stack is %p..%p)\n",
+				 name, (void *)address, info.begin, info.end);
+		}
+	}
+#endif
+
 	pr_emerg("PANIC: double fault, error_code: 0x%lx\n", error_code);
 	die("double fault", regs, error_code);
 	panic("Machine halted.");
@@ -708,7 +721,9 @@ asmlinkage __visible noinstr struct pt_r
 	sp    = regs->sp;
 	stack = (unsigned long *)sp;
 
-	if (!get_stack_info_noinstr(stack, current, &info) || info.type == STACK_TYPE_ENTRY ||
+	if (!get_stack_info_noinstr(stack, current, &info) ||
+	    info.type & STACK_TYPE_GUARD ||
+	    info.type == STACK_TYPE_ENTRY ||
 	    info.type >= STACK_TYPE_EXCEPTION_LAST)
 		sp = __this_cpu_ist_top_va(VC2);