Commit b08418b5 authored by Josh Poimboeuf's avatar Josh Poimboeuf Committed by Ingo Molnar
Browse files

x86/unwind: Prevent false warnings for non-current tasks 



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: default avatarMiroslav Benes <mbenes@suse.cz>
Signed-off-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: default avatarIngo 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
parent 153eb222

arch/x86/kernel/dumpstack_64.c

+2 −1
Original line number Diff line number Diff line
@@ -183,6 +183,7 @@ recursion_check: 
	 */

	if (visit_mask) {

		if (*visit_mask & (1UL << info->type)) {

			if (task == current)

				printk_deferred_once(KERN_WARNING "WARNING: stack recursion on stack type %d\n", info->type);

			goto unknown;

		}

arch/x86/kernel/unwind_frame.c

+3 −0
Original line number Diff line number Diff line
@@ -344,6 +344,9 @@ 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",

arch/x86/kernel/unwind_orc.c

+23 −17
Original line number Diff line number Diff line
@@ -8,7 +8,13 @@ 
#include <asm/orc_lookup.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[];
@@ -446,7 +452,7 @@ bool unwind_next_frame(struct unwind_state *state) 


	case ORC_REG_R10:

		if (!state->regs || !state->full_regs) {

			orc_warn("missing regs for base reg R10 at ip %pB\n",

			orc_warn_current("missing R10 value at %pB\n",

					 (void *)state->ip);

			goto err;

		}
@@ -455,7 +461,7 @@ bool unwind_next_frame(struct unwind_state *state) 


	case ORC_REG_R13:

		if (!state->regs || !state->full_regs) {

			orc_warn("missing regs for base reg R13 at ip %pB\n",

			orc_warn_current("missing R13 value at %pB\n",

					 (void *)state->ip);

			goto err;

		}
@@ -464,7 +470,7 @@ bool unwind_next_frame(struct unwind_state *state) 


	case ORC_REG_DI:

		if (!state->regs || !state->full_regs) {

			orc_warn("missing regs for base reg DI at ip %pB\n",

			orc_warn_current("missing RDI value at %pB\n",

					 (void *)state->ip);

			goto err;

		}
@@ -473,7 +479,7 @@ bool unwind_next_frame(struct unwind_state *state) 


	case ORC_REG_DX:

		if (!state->regs || !state->full_regs) {

			orc_warn("missing regs for base reg DX at ip %pB\n",

			orc_warn_current("missing DX value at %pB\n",

					 (void *)state->ip);

			goto err;

		}
@@ -481,7 +487,7 @@ bool unwind_next_frame(struct unwind_state *state) 
		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 err;

	}
@@ -509,8 +515,8 @@ bool unwind_next_frame(struct unwind_state *state) 


	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 err;

		}
@@ -521,8 +527,8 @@ bool unwind_next_frame(struct unwind_state *state) 


	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 err;

		}
@@ -532,7 +538,7 @@ bool unwind_next_frame(struct unwind_state *state) 
		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;

	}
@@ -564,7 +570,7 @@ bool unwind_next_frame(struct unwind_state *state) 
	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",

		orc_warn_current("stack going in the wrong direction? at %pB\n",

				 (void *)orig_ip);

		goto err;

	}

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