[PATCH v2 03/18] x86/dumpstack: Add get_stack_info() support for the SYSENTER stack

[Andy Lutomirski <luto@kernel.org>]

get_stack_info() doesn't currently know about the SYSENTER stack, so
unwinding will fail if we entered the kernel on the SYSENTER stack
and haven't fully switched off.  Teach get_stack_info() about the
SYSENTER stack.

With future patches applied that run part of the entry code on the
SYSENTER stack and introduce an intentional BUG(), I would get:

[    3.962218] PANIC: double fault, error_code: 0x0
...
[    3.963998] task: ffff88001aa18000 task.stack: ffff88001aa20000
[    3.964526] RIP: 0010:do_error_trap+0x33/0x1c0
[    3.964947] RSP: 0000:ffffffffff1b8f78 EFLAGS: 00010096
[    3.965439] RAX: dffffc0000000000 RBX: ffffffffff1b8f90 RCX: 0000000000000006
[    3.966067] RDX: ffffffff82048b20 RSI: 0000000000000000 RDI: ffffffffff1b9110
[    3.966696] RBP: ffffffffff1b9088 R08: 0000000000000004 R09: 0000000000000000
[    3.967316] R10: 0000000000000000 R11: fffffbffffe3723f R12: 0000000000000006
[    3.967939] R13: 0000000000000000 R14: 0000000000000004 R15: 0000000000000000
[    3.968565] FS:  0000000000000000(0000) GS:ffff88001ae00000(0000) knlGS:0000000000000000
[    3.969272] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    3.969776] CR2: ffffffffff1b8f68 CR3: 0000000019308002 CR4: 00000000003606f0
[    3.970406] Call Trace:
[    3.970632] Code: ...

With this patch, I get:

[    4.211553] PANIC: double fault, error_code: 0x0
...
[    4.213536] task: ffff88001aa18000 task.stack: ffff88001aa20000
[    4.214059] RIP: 0010:do_error_trap+0x33/0x1c0
[    4.214449] RSP: 0000:ffffffffff1b8f78 EFLAGS: 00010096
[    4.214934] RAX: dffffc0000000000 RBX: ffffffffff1b8f90 RCX: 0000000000000006
[    4.215554] RDX: ffffffff82048b20 RSI: 0000000000000000 RDI: ffffffffff1b9110
[    4.216176] RBP: ffffffffff1b9088 R08: 0000000000000004 R09: 0000000000000000
[    4.216793] R10: 0000000000000000 R11: fffffbffffe3723f R12: 0000000000000006
[    4.217419] R13: 0000000000000000 R14: 0000000000000004 R15: 0000000000000000
[    4.218046] FS:  0000000000000000(0000) GS:ffff88001ae00000(0000) knlGS:0000000000000000
[    4.218775] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    4.219280] CR2: ffffffffff1b8f68 CR3: 00000000193da002 CR4: 00000000003606f0
[    4.219931] Call Trace:
[    4.220156]  <SYSENTER>
[    4.220383]  ? async_page_fault+0x36/0x60
[    4.220768]  ? invalid_op+0x22/0x40
[    4.221087]  ? async_page_fault+0x36/0x60
[    4.221442]  ? sync_regs+0x3c/0x40
[    4.221745]  ? sync_regs+0x2e/0x40
[    4.222051]  ? error_entry+0x6c/0xd0
[    4.222395]  ? async_page_fault+0x36/0x60
[    4.222748]  </SYSENTER>
[    4.223014] Code: ...

Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
 arch/x86/include/asm/stacktrace.h |  3 +++
 arch/x86/kernel/dumpstack.c       | 19 +++++++++++++++++++
 arch/x86/kernel/dumpstack_32.c    |  6 ++++++
 arch/x86/kernel/dumpstack_64.c    |  6 ++++++
 4 files changed, 34 insertions(+)

diff --git a/arch/x86/include/asm/stacktrace.h b/arch/x86/include/asm/stacktrace.h
index 8da111b3c342..f8062bfd43a0 100644
--- a/arch/x86/include/asm/stacktrace.h
+++ b/arch/x86/include/asm/stacktrace.h
@@ -16,6 +16,7 @@ enum stack_type {
 	STACK_TYPE_TASK,
 	STACK_TYPE_IRQ,
 	STACK_TYPE_SOFTIRQ,
+	STACK_TYPE_SYSENTER,
 	STACK_TYPE_EXCEPTION,
 	STACK_TYPE_EXCEPTION_LAST = STACK_TYPE_EXCEPTION + N_EXCEPTION_STACKS-1,
 };
@@ -28,6 +29,8 @@ struct stack_info {
 bool in_task_stack(unsigned long *stack, struct task_struct *task,
 		   struct stack_info *info);
 
+bool in_sysenter_stack(unsigned long *stack, struct stack_info *info);
+
 int get_stack_info(unsigned long *stack, struct task_struct *task,
 		   struct stack_info *info, unsigned long *visit_mask);
 
diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
index f13b4c00a5de..5e7d10e8ca25 100644
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -43,6 +43,25 @@ bool in_task_stack(unsigned long *stack, struct task_struct *task,
 	return true;
 }
 
+bool in_sysenter_stack(unsigned long *stack, struct stack_info *info)
+{
+	struct tss_struct *tss = this_cpu_ptr(&cpu_tss);
+
+	/* Treat the canary as part of the stack for unwinding purposes. */
+	void *begin = &tss->SYSENTER_stack_canary;
+	void *end = (void *)&tss->SYSENTER_stack + sizeof(tss->SYSENTER_stack);
+
+	if ((void *)stack < begin || (void *)stack >= end)
+		return false;
+
+	info->type	= STACK_TYPE_SYSENTER;
+	info->begin	= begin;
+	info->end	= end;
+	info->next_sp	= NULL;
+
+	return true;
+}
+
 static void printk_stack_address(unsigned long address, int reliable,
 				 char *log_lvl)
 {
diff --git a/arch/x86/kernel/dumpstack_32.c b/arch/x86/kernel/dumpstack_32.c
index daefae83a3aa..5ff13a6b3680 100644
--- a/arch/x86/kernel/dumpstack_32.c
+++ b/arch/x86/kernel/dumpstack_32.c
@@ -26,6 +26,9 @@ const char *stack_type_name(enum stack_type type)
 	if (type == STACK_TYPE_SOFTIRQ)
 		return "SOFTIRQ";
 
+	if (type == STACK_TYPE_SYSENTER)
+		return "SYSENTER";
+
 	return NULL;
 }
 
@@ -93,6 +96,9 @@ int get_stack_info(unsigned long *stack, struct task_struct *task,
 	if (task != current)
 		goto unknown;
 
+	if (in_sysenter_stack(stack, info))
+		goto recursion_check;
+
 	if (in_hardirq_stack(stack, info))
 		goto recursion_check;
 
diff --git a/arch/x86/kernel/dumpstack_64.c b/arch/x86/kernel/dumpstack_64.c
index 88ce2ffdb110..abc828f8c297 100644
--- a/arch/x86/kernel/dumpstack_64.c
+++ b/arch/x86/kernel/dumpstack_64.c
@@ -37,6 +37,9 @@ const char *stack_type_name(enum stack_type type)
 	if (type == STACK_TYPE_IRQ)
 		return "IRQ";
 
+	if (type == STACK_TYPE_SYSENTER)
+		return "SYSENTER";
+
 	if (type >= STACK_TYPE_EXCEPTION && type <= STACK_TYPE_EXCEPTION_LAST)
 		return exception_stack_names[type - STACK_TYPE_EXCEPTION];
 
@@ -115,6 +118,9 @@ int get_stack_info(unsigned long *stack, struct task_struct *task,
 	if (in_irq_stack(stack, info))
 		goto recursion_check;
 
+	if (in_sysenter_stack(stack, info))
+		goto recursion_check;
+
 	goto unknown;
 
 recursion_check:
-- 
2.13.6