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SubjectRe: [PATCH 1/2] x86/stacktrace: do not fail when regs on stack for ORC
On Wed, Dec 20, 2017 at 08:07:17PM +0100, Jiri Slaby wrote:
> On 12/20/2017, 06:45 PM, Josh Poimboeuf wrote:
> > It might not be until 2018 though. But in the meantime you can go ahead
> > and update your patches accordingly and then we can combine them for
> > testing next year.
>
> I already did ;). So when you have that ready, I will send it on top
> right after.

Sorry for the delay... Here's a (lightly tested) patch. Can you test
it with the latest version of your patches?

----

From: Josh Poimboeuf <jpoimboe@redhat.com>
Subject: [PATCH] x86/unwind/orc: Detect the end of the stack

The existing UNWIND_HINT_EMPTY annotations happen to be good indicators
of where entry code calls into C code for the first time. So also use
them to mark the end of the stack for the ORC unwinder.

Use that information to set unwind->error if the ORC unwinder doesn't
unwind all the way to the end. This will be needed for enabling
HAVE_RELIABLE_STACKTRACE for the ORC unwinder so we can use it with the
livepatch consistency model.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
arch/x86/entry/entry_64.S | 1 +
arch/x86/include/asm/orc_types.h | 2 ++
arch/x86/include/asm/unwind_hints.h | 16 +++++----
arch/x86/kernel/unwind_orc.c | 50 ++++++++++++++++----------
tools/objtool/arch/x86/include/asm/orc_types.h | 2 ++
5 files changed, 46 insertions(+), 25 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index ab4f451aeb97..e35dbc507425 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -408,6 +408,7 @@ ENTRY(ret_from_fork)

1:
/* kernel thread */
+ UNWIND_HINT_EMPTY
movq %r12, %rdi
CALL_NOSPEC %rbx
/*
diff --git a/arch/x86/include/asm/orc_types.h b/arch/x86/include/asm/orc_types.h
index 9c9dc579bd7d..46f516dd80ce 100644
--- a/arch/x86/include/asm/orc_types.h
+++ b/arch/x86/include/asm/orc_types.h
@@ -88,6 +88,7 @@ struct orc_entry {
unsigned sp_reg:4;
unsigned bp_reg:4;
unsigned type:2;
+ unsigned end:1;
} __packed;

/*
@@ -101,6 +102,7 @@ struct unwind_hint {
s16 sp_offset;
u8 sp_reg;
u8 type;
+ u8 end;
};
#endif /* __ASSEMBLY__ */

diff --git a/arch/x86/include/asm/unwind_hints.h b/arch/x86/include/asm/unwind_hints.h
index bae46fc6b9de..0bcdb1279361 100644
--- a/arch/x86/include/asm/unwind_hints.h
+++ b/arch/x86/include/asm/unwind_hints.h
@@ -26,7 +26,7 @@
* the debuginfo as necessary. It will also warn if it sees any
* inconsistencies.
*/
-.macro UNWIND_HINT sp_reg=ORC_REG_SP sp_offset=0 type=ORC_TYPE_CALL
+.macro UNWIND_HINT sp_reg=ORC_REG_SP sp_offset=0 type=ORC_TYPE_CALL end=0
#ifdef CONFIG_STACK_VALIDATION
.Lunwind_hint_ip_\@:
.pushsection .discard.unwind_hints
@@ -35,12 +35,14 @@
.short \sp_offset
.byte \sp_reg
.byte \type
+ .byte \end
+ .balign 4
.popsection
#endif
.endm

.macro UNWIND_HINT_EMPTY
- UNWIND_HINT sp_reg=ORC_REG_UNDEFINED
+ UNWIND_HINT sp_reg=ORC_REG_UNDEFINED end=1
.endm

.macro UNWIND_HINT_REGS base=%rsp offset=0 indirect=0 extra=1 iret=0
@@ -86,19 +88,21 @@

#else /* !__ASSEMBLY__ */

-#define UNWIND_HINT(sp_reg, sp_offset, type) \
+#define UNWIND_HINT(sp_reg, sp_offset, type, end) \
"987: \n\t" \
".pushsection .discard.unwind_hints\n\t" \
/* struct unwind_hint */ \
".long 987b - .\n\t" \
- ".short " __stringify(sp_offset) "\n\t" \
+ ".short " __stringify(sp_offset) "\n\t" \
".byte " __stringify(sp_reg) "\n\t" \
".byte " __stringify(type) "\n\t" \
+ ".byte " __stringify(end) "\n\t" \
+ ".balign 4 \n\t" \
".popsection\n\t"

-#define UNWIND_HINT_SAVE UNWIND_HINT(0, 0, UNWIND_HINT_TYPE_SAVE)
+#define UNWIND_HINT_SAVE UNWIND_HINT(0, 0, UNWIND_HINT_TYPE_SAVE, 0)

-#define UNWIND_HINT_RESTORE UNWIND_HINT(0, 0, UNWIND_HINT_TYPE_RESTORE)
+#define UNWIND_HINT_RESTORE UNWIND_HINT(0, 0, UNWIND_HINT_TYPE_RESTORE, 0)

#endif /* __ASSEMBLY__ */

diff --git a/arch/x86/kernel/unwind_orc.c b/arch/x86/kernel/unwind_orc.c
index feb28fee6cea..8dd7f1fa3885 100644
--- a/arch/x86/kernel/unwind_orc.c
+++ b/arch/x86/kernel/unwind_orc.c
@@ -352,7 +352,7 @@ static bool deref_stack_iret_regs(struct unwind_state *state, unsigned long addr

bool unwind_next_frame(struct unwind_state *state)
{
- unsigned long ip_p, sp, orig_ip, prev_sp = state->sp;
+ unsigned long ip_p, sp, orig_ip = state->ip, prev_sp = state->sp;
enum stack_type prev_type = state->stack_info.type;
struct orc_entry *orc;
bool indirect = false;
@@ -363,7 +363,7 @@ bool unwind_next_frame(struct unwind_state *state)
/* Don't let modules unload while we're reading their ORC data. */
preempt_disable();

- /* Have we reached the end? */
+ /* End-of-stack check for user tasks: */
if (state->regs && user_mode(state->regs))
goto done;

@@ -374,9 +374,16 @@ bool unwind_next_frame(struct unwind_state *state)
* calls and calls to noreturn functions.
*/
orc = orc_find(state->signal ? state->ip : state->ip - 1);
- if (!orc || orc->sp_reg == ORC_REG_UNDEFINED)
- goto done;
- orig_ip = state->ip;
+ if (!orc)
+ goto err;
+
+ /* End-of-stack check for kernel threads: */
+ if (orc->sp_reg == ORC_REG_UNDEFINED) {
+ if (!orc->end)
+ goto err;
+
+ goto the_end;
+ }

/* Find the previous frame's stack: */
switch (orc->sp_reg) {
@@ -402,7 +409,7 @@ bool unwind_next_frame(struct unwind_state *state)
if (!state->regs || !state->full_regs) {
orc_warn("missing regs for base reg R10 at ip %pB\n",
(void *)state->ip);
- goto done;
+ goto err;
}
sp = state->regs->r10;
break;
@@ -411,7 +418,7 @@ bool unwind_next_frame(struct unwind_state *state)
if (!state->regs || !state->full_regs) {
orc_warn("missing regs for base reg R13 at ip %pB\n",
(void *)state->ip);
- goto done;
+ goto err;
}
sp = state->regs->r13;
break;
@@ -420,7 +427,7 @@ bool unwind_next_frame(struct unwind_state *state)
if (!state->regs || !state->full_regs) {
orc_warn("missing regs for base reg DI at ip %pB\n",
(void *)state->ip);
- goto done;
+ goto err;
}
sp = state->regs->di;
break;
@@ -429,7 +436,7 @@ bool unwind_next_frame(struct unwind_state *state)
if (!state->regs || !state->full_regs) {
orc_warn("missing regs for base reg DX at ip %pB\n",
(void *)state->ip);
- goto done;
+ goto err;
}
sp = state->regs->dx;
break;
@@ -437,12 +444,12 @@ bool unwind_next_frame(struct unwind_state *state)
default:
orc_warn("unknown SP base reg %d for ip %pB\n",
orc->sp_reg, (void *)state->ip);
- goto done;
+ goto err;
}

if (indirect) {
if (!deref_stack_reg(state, sp, &sp))
- goto done;
+ goto err;
}

/* Find IP, SP and possibly regs: */
@@ -451,7 +458,7 @@ bool unwind_next_frame(struct unwind_state *state)
ip_p = sp - sizeof(long);

if (!deref_stack_reg(state, ip_p, &state->ip))
- goto done;
+ goto err;

state->ip = ftrace_graph_ret_addr(state->task, &state->graph_idx,
state->ip, (void *)ip_p);
@@ -465,7 +472,7 @@ bool unwind_next_frame(struct unwind_state *state)
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);
- goto done;
+ goto err;
}

state->regs = (struct pt_regs *)sp;
@@ -477,7 +484,7 @@ bool unwind_next_frame(struct unwind_state *state)
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);
- goto done;
+ goto err;
}

state->regs = (void *)sp - IRET_FRAME_OFFSET;
@@ -500,18 +507,18 @@ bool unwind_next_frame(struct unwind_state *state)

case ORC_REG_PREV_SP:
if (!deref_stack_reg(state, sp + orc->bp_offset, &state->bp))
- goto done;
+ goto err;
break;

case ORC_REG_BP:
if (!deref_stack_reg(state, state->bp + orc->bp_offset, &state->bp))
- goto done;
+ goto err;
break;

default:
orc_warn("unknown BP base reg %d for ip %pB\n",
orc->bp_reg, (void *)orig_ip);
- goto done;
+ goto err;
}

/* Prevent a recursive loop due to bad ORC data: */
@@ -520,16 +527,21 @@ bool unwind_next_frame(struct unwind_state *state)
state->sp <= prev_sp) {
orc_warn("stack going in the wrong direction? ip=%pB\n",
(void *)orig_ip);
- goto done;
+ goto err;
}

preempt_enable();
return true;

-done:
+err:
+ state->error = true;
+
+the_end:
preempt_enable();
state->stack_info.type = STACK_TYPE_UNKNOWN;
return false;
+
+
}
EXPORT_SYMBOL_GPL(unwind_next_frame);

diff --git a/tools/objtool/arch/x86/include/asm/orc_types.h b/tools/objtool/arch/x86/include/asm/orc_types.h
index 9c9dc579bd7d..46f516dd80ce 100644
--- a/tools/objtool/arch/x86/include/asm/orc_types.h
+++ b/tools/objtool/arch/x86/include/asm/orc_types.h
@@ -88,6 +88,7 @@ struct orc_entry {
unsigned sp_reg:4;
unsigned bp_reg:4;
unsigned type:2;
+ unsigned end:1;
} __packed;

/*
@@ -101,6 +102,7 @@ struct unwind_hint {
s16 sp_offset;
u8 sp_reg;
u8 type;
+ u8 end;
};
#endif /* __ASSEMBLY__ */

--
2.14.3
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