From: Josh Poimboeuf <jpoimboe@redhat.com>
Date: Sat, 25 Apr 2020 05:03:06 -0500
Subject: x86/unwind: Prevent false warnings for non-current tasks
Git-commit: b08418b54831255a7e3700d6bf7dfc2bdae25cd7
Patch-mainline: v5.7-rc5
References: bsc#1058115

There's some daring kernel code out there which dumps the stack of
another task without first making sure the task is inactive.  If the
task happens to be running while the unwinder is reading the stack,
unusual unwinder warnings can result.

There's no race-free way for the unwinder to know whether such a warning
is legitimate, so just disable unwinder warnings for all non-current
tasks.

Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Dave Jones <dsj@fb.com>
Cc: Jann Horn <jannh@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Link: https://lore.kernel.org/r/ec424a2aea1d461eb30cab48a28c6433de2ab784.1587808742.git.jpoimboe@redhat.com

Acked-by: Miroslav Benes <mbenes@suse.cz>
---
 arch/x86/kernel/dumpstack_64.c |    3 ++-
 arch/x86/kernel/unwind_frame.c |    3 +++
 arch/x86/kernel/unwind_orc.c   |   40 +++++++++++++++++++++++-----------------
 3 files changed, 28 insertions(+), 18 deletions(-)

--- a/arch/x86/kernel/dumpstack_64.c
+++ b/arch/x86/kernel/dumpstack_64.c
@@ -136,7 +136,8 @@ recursion_check:
 	 */
 	if (visit_mask) {
 		if (*visit_mask & (1UL << info->type)) {
-			printk_deferred_once(KERN_WARNING "WARNING: stack recursion on stack type %d\n", info->type);
+			if (task == current)
+				printk_deferred_once(KERN_WARNING "WARNING: stack recursion on stack type %d\n", info->type);
 			goto unknown;
 		}
 		*visit_mask |= 1UL << info->type;
--- a/arch/x86/kernel/unwind_frame.c
+++ b/arch/x86/kernel/unwind_frame.c
@@ -366,6 +366,9 @@ bad_address:
 	if (IS_ENABLED(CONFIG_X86_32))
 		goto the_end;
 
+	if (state->task != current)
+		goto the_end;
+
 	if (state->regs) {
 		printk_deferred_once(KERN_WARNING
 			"WARNING: kernel stack regs at %p in %s:%d has bad 'bp' value %p\n",
--- a/arch/x86/kernel/unwind_orc.c
+++ b/arch/x86/kernel/unwind_orc.c
@@ -8,7 +8,13 @@
 #include <asm/sections.h>
 
 #define orc_warn(fmt, ...) \
-	printk_deferred_once(KERN_WARNING pr_fmt("WARNING: " fmt), ##__VA_ARGS__)
+	printk_deferred_once(KERN_WARNING "WARNING: " fmt, ##__VA_ARGS__)
+
+#define orc_warn_current(args...)					\
+({									\
+	if (state->task == current)					\
+		orc_warn(args);						\
+})
 
 extern int __start_orc_unwind_ip[];
 extern int __stop_orc_unwind_ip[];
@@ -418,8 +424,8 @@ bool unwind_next_frame(struct unwind_sta
 
 	case ORC_REG_R10:
 		if (!state->regs || !state->full_regs) {
-			orc_warn("missing regs for base reg R10 at ip %pB\n",
-				 (void *)state->ip);
+			orc_warn_current("missing R10 value at %pB\n",
+					 (void *)state->ip);
 			goto done;
 		}
 		sp = state->regs->r10;
@@ -427,8 +433,8 @@ bool unwind_next_frame(struct unwind_sta
 
 	case ORC_REG_R13:
 		if (!state->regs || !state->full_regs) {
-			orc_warn("missing regs for base reg R13 at ip %pB\n",
-				 (void *)state->ip);
+			orc_warn_current("missing R13 value at %pB\n",
+					 (void *)state->ip);
 			goto done;
 		}
 		sp = state->regs->r13;
@@ -436,8 +442,8 @@ bool unwind_next_frame(struct unwind_sta
 
 	case ORC_REG_DI:
 		if (!state->regs || !state->full_regs) {
-			orc_warn("missing regs for base reg DI at ip %pB\n",
-				 (void *)state->ip);
+			orc_warn_current("missing RDI value at %pB\n",
+					 (void *)state->ip);
 			goto done;
 		}
 		sp = state->regs->di;
@@ -445,15 +451,15 @@ bool unwind_next_frame(struct unwind_sta
 
 	case ORC_REG_DX:
 		if (!state->regs || !state->full_regs) {
-			orc_warn("missing regs for base reg DX at ip %pB\n",
-				 (void *)state->ip);
+			orc_warn_current("missing DX value at %pB\n",
+					 (void *)state->ip);
 			goto done;
 		}
 		sp = state->regs->dx;
 		break;
 
 	default:
-		orc_warn("unknown SP base reg %d for ip %pB\n",
+		orc_warn("unknown SP base reg %d at %pB\n",
 			 orc->sp_reg, (void *)state->ip);
 		goto done;
 	}
@@ -481,8 +487,8 @@ bool unwind_next_frame(struct unwind_sta
 
 	case ORC_TYPE_REGS:
 		if (!deref_stack_regs(state, sp, &state->ip, &state->sp)) {
-			orc_warn("can't dereference registers at %p for ip %pB\n",
-				 (void *)sp, (void *)orig_ip);
+			orc_warn_current("can't access registers at %pB\n",
+					 (void *)orig_ip);
 			goto done;
 		}
 
@@ -493,8 +499,8 @@ bool unwind_next_frame(struct unwind_sta
 
 	case ORC_TYPE_REGS_IRET:
 		if (!deref_stack_iret_regs(state, sp, &state->ip, &state->sp)) {
-			orc_warn("can't dereference iret registers at %p for ip %pB\n",
-				 (void *)sp, (void *)orig_ip);
+			orc_warn_current("can't access iret registers at %pB\n",
+					 (void *)orig_ip);
 			goto done;
 		}
 
@@ -504,7 +510,7 @@ bool unwind_next_frame(struct unwind_sta
 		break;
 
 	default:
-		orc_warn("unknown .orc_unwind entry type %d for ip %pB\n",
+		orc_warn("unknown .orc_unwind entry type %d at %pB\n",
 			 orc->type, (void *)orig_ip);
 		break;
 	}
@@ -536,8 +542,8 @@ bool unwind_next_frame(struct unwind_sta
 	if (state->stack_info.type == prev_type &&
 	    on_stack(&state->stack_info, (void *)state->sp, sizeof(long)) &&
 	    state->sp <= prev_sp) {
-		orc_warn("stack going in the wrong direction? ip=%pB\n",
-			 (void *)orig_ip);
+		orc_warn_current("stack going in the wrong direction? at %pB\n",
+				 (void *)orig_ip);
 		goto done;
 	}