[PATCH v2 5/6] x86/unwind/orc: Detect the end of the stack

From: Jiri Slaby
Date: Mon May 14 2018 - 10:07:53 EST

From: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>

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.

Thanks to Jiri Slaby for teaching the ORCs about the unwind hints.

[v2] this patch is new in v2

Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
---
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 | 52 +++++++++++++++-----------
tools/objtool/arch/x86/include/asm/orc_types.h | 2 +
tools/objtool/check.c | 1 +
tools/objtool/check.h | 2 +-
tools/objtool/orc_dump.c | 3 +-
tools/objtool/orc_gen.c | 2 +
9 files changed, 52 insertions(+), 29 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 49109c991f87..5acdb7946d69 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -410,6 +410,7 @@ SYM_CODE_START(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..26038eacf74a 100644
--- a/arch/x86/kernel/unwind_orc.c
+++ b/arch/x86/kernel/unwind_orc.c
@@ -198,7 +198,7 @@ static int orc_sort_cmp(const void *_a, const void *_b)
* whitelisted .o files which didn't get objtool generation.
*/
orc_a = cur_orc_table + (a - cur_orc_ip_table);
- return orc_a->sp_reg == ORC_REG_UNDEFINED ? -1 : 1;
+ return orc_a->sp_reg == ORC_REG_UNDEFINED && !orc_a->end ? -1 : 1;
}

#ifdef CONFIG_MODULES
@@ -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;
@@ -363,9 +363,9 @@ 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;
+ goto the_end;

/*
* Find the orc_entry associated with the text address.
@@ -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: */
@@ -520,13 +527,16 @@ 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;
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__ */

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 5409f6f6c48d..fef15cea9f1e 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1109,6 +1109,7 @@ static int read_unwind_hints(struct objtool_file *file)

cfa->offset = hint->sp_offset;
insn->state.type = hint->type;
+ insn->state.end = hint->end;
}

return 0;
diff --git a/tools/objtool/check.h b/tools/objtool/check.h
index c6b68fcb926f..95700a2bcb7c 100644
--- a/tools/objtool/check.h
+++ b/tools/objtool/check.h
@@ -31,7 +31,7 @@ struct insn_state {
int stack_size;
unsigned char type;
bool bp_scratch;
- bool drap;
+ bool drap, end;
int drap_reg, drap_offset;
struct cfi_reg vals[CFI_NUM_REGS];
};
diff --git a/tools/objtool/orc_dump.c b/tools/objtool/orc_dump.c
index c3343820916a..faa444270ee3 100644
--- a/tools/objtool/orc_dump.c
+++ b/tools/objtool/orc_dump.c
@@ -203,7 +203,8 @@ int orc_dump(const char *_objname)

print_reg(orc[i].bp_reg, orc[i].bp_offset);

- printf(" type:%s\n", orc_type_name(orc[i].type));
+ printf(" type:%s end:%d\n",
+ orc_type_name(orc[i].type), orc[i].end);
}

elf_end(elf);
diff --git a/tools/objtool/orc_gen.c b/tools/objtool/orc_gen.c
index 18384d9be4e1..3f98dcfbc177 100644
--- a/tools/objtool/orc_gen.c
+++ b/tools/objtool/orc_gen.c
@@ -31,6 +31,8 @@ int create_orc(struct objtool_file *file)
struct cfi_reg *cfa = &insn->state.cfa;
struct cfi_reg *bp = &insn->state.regs[CFI_BP];

+ orc->end = insn->state.end;
+
if (cfa->base == CFI_UNDEFINED) {
orc->sp_reg = ORC_REG_UNDEFINED;
continue;
--
2.16.3