[PATCH 5.10 008/148] objtool: Combine UNWIND_HINT_RET_OFFSET and UNWIND_HINT_FUNC

Greg Kroah-Hartman
2022-07-23T09:57:15Z

From: Josh Poimboeuf <jpoimboe@redhat.com>

commit b735bd3e68824316655252a931a3353a6ebc036f upstream.

The ORC metadata generated for UNWIND_HINT_FUNC isn't actually very
func-like. With certain usages it can cause stack state mismatches
because it doesn't set the return address (CFI_RA).

Also, users of UNWIND_HINT_RET_OFFSET no longer need to set a custom
return stack offset. Instead they just need to specify a func-like
situation, so the current ret_offset code is hacky for no good reason.

Solve both problems by simplifying the RET_OFFSET handling and
converting it into a more useful UNWIND_HINT_FUNC.

If we end up needing the old 'ret_offset' functionality again in the
future, we should be able to support it pretty easily with the addition
of a custom 'sp_offset' in UNWIND_HINT_FUNC.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/db9d1f5d79dddfbb3725ef6d8ec3477ad199948d.1611263462.git.jpoimboe@redhat.com
[bwh: Backported to 5.10:
- Don't use bswap_if_needed() since we don't have any of the other fixes
for mixed-endian cross-compilation
- Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/include/asm/unwind_hints.h | 13 +-----------
arch/x86/kernel/ftrace_64.S | 2 -
arch/x86/lib/retpoline.S | 2 -
include/linux/objtool.h | 5 +++-
tools/include/linux/objtool.h | 5 +++-
tools/objtool/arch/x86/decode.c | 4 +--
tools/objtool/check.c | 37 ++++++++++++++----------------------
tools/objtool/check.h | 1
8 files changed, 29 insertions(+), 40 deletions(-)

--- a/arch/x86/include/asm/unwind_hints.h
+++ b/arch/x86/include/asm/unwind_hints.h
@@ -48,17 +48,8 @@
UNWIND_HINT_REGS base=\base offset=\offset partial=1
.endm

-.macro UNWIND_HINT_FUNC sp_offset=8
- UNWIND_HINT sp_reg=ORC_REG_SP sp_offset=\sp_offset type=UNWIND_HINT_TYPE_CALL
-.endm
-
-/*
- * RET_OFFSET: Used on instructions that terminate a function; mostly RETURN
- * and sibling calls. On these, sp_offset denotes the expected offset from
- * initial_func_cfi.
- */
-.macro UNWIND_HINT_RET_OFFSET sp_offset=8
- UNWIND_HINT sp_reg=ORC_REG_SP type=UNWIND_HINT_TYPE_RET_OFFSET sp_offset=\sp_offset
+.macro UNWIND_HINT_FUNC
+ UNWIND_HINT sp_reg=ORC_REG_SP sp_offset=8 type=UNWIND_HINT_TYPE_FUNC
.endm

#endif /* __ASSEMBLY__ */
--- a/arch/x86/kernel/ftrace_64.S
+++ b/arch/x86/kernel/ftrace_64.S
@@ -265,7 +265,7 @@ SYM_INNER_LABEL(ftrace_regs_caller_end,
restore_mcount_regs 8
/* Restore flags */
popfq
- UNWIND_HINT_RET_OFFSET
+ UNWIND_HINT_FUNC
jmp ftrace_epilogue

SYM_FUNC_END(ftrace_regs_caller)
--- a/arch/x86/lib/retpoline.S
+++ b/arch/x86/lib/retpoline.S
@@ -28,7 +28,7 @@ SYM_FUNC_START_NOALIGN(__x86_retpoline_\
jmp .Lspec_trap_\@
.Ldo_rop_\@:
mov %\reg, (%_ASM_SP)
- UNWIND_HINT_RET_OFFSET
+ UNWIND_HINT_FUNC
ret
SYM_FUNC_END(__x86_retpoline_\reg)

--- a/include/linux/objtool.h
+++ b/include/linux/objtool.h
@@ -29,11 +29,14 @@ struct unwind_hint {
*
* UNWIND_HINT_TYPE_REGS_PARTIAL: Used in entry code to indicate that
* sp_reg+sp_offset points to the iret return frame.
+ *
+ * UNWIND_HINT_FUNC: Generate the unwind metadata of a callable function.
+ * Useful for code which doesn't have an ELF function annotation.
*/
#define UNWIND_HINT_TYPE_CALL 0
#define UNWIND_HINT_TYPE_REGS 1
#define UNWIND_HINT_TYPE_REGS_PARTIAL 2
-#define UNWIND_HINT_TYPE_RET_OFFSET 3
+#define UNWIND_HINT_TYPE_FUNC 3

#ifdef CONFIG_STACK_VALIDATION

--- a/tools/include/linux/objtool.h
+++ b/tools/include/linux/objtool.h
@@ -29,11 +29,14 @@ struct unwind_hint {
*
* UNWIND_HINT_TYPE_REGS_PARTIAL: Used in entry code to indicate that
* sp_reg+sp_offset points to the iret return frame.
+ *
+ * UNWIND_HINT_FUNC: Generate the unwind metadata of a callable function.
+ * Useful for code which doesn't have an ELF function annotation.
*/
#define UNWIND_HINT_TYPE_CALL 0
#define UNWIND_HINT_TYPE_REGS 1
#define UNWIND_HINT_TYPE_REGS_PARTIAL 2
-#define UNWIND_HINT_TYPE_RET_OFFSET 3
+#define UNWIND_HINT_TYPE_FUNC 3

#ifdef CONFIG_STACK_VALIDATION

--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -563,8 +563,8 @@ void arch_initial_func_cfi_state(struct
state->cfa.offset = 8;

/* initial RA (return address) */
- state->regs[16].base = CFI_CFA;
- state->regs[16].offset = -8;
+ state->regs[CFI_RA].base = CFI_CFA;
+ state->regs[CFI_RA].offset = -8;
}

const char *arch_nop_insn(int len)
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1423,13 +1423,20 @@ static int add_jump_table_alts(struct ob
return 0;
}

+static void set_func_state(struct cfi_state *state)
+{
+ state->cfa = initial_func_cfi.cfa;
+ memcpy(&state->regs, &initial_func_cfi.regs,
+ CFI_NUM_REGS * sizeof(struct cfi_reg));
+ state->stack_size = initial_func_cfi.cfa.offset;
+}
+
static int read_unwind_hints(struct objtool_file *file)
{
struct section *sec, *relocsec;
struct reloc *reloc;
struct unwind_hint *hint;
struct instruction *insn;
- struct cfi_reg *cfa;
int i;

sec = find_section_by_name(file->elf, ".discard.unwind_hints");
@@ -1464,22 +1471,20 @@ static int read_unwind_hints(struct objt
return -1;
}

- cfa = &insn->cfi.cfa;
+ insn->hint = true;

- if (hint->type == UNWIND_HINT_TYPE_RET_OFFSET) {
- insn->ret_offset = hint->sp_offset;
+ if (hint->type == UNWIND_HINT_TYPE_FUNC) {
+ set_func_state(&insn->cfi);
continue;
}

- insn->hint = true;
-
if (arch_decode_hint_reg(insn, hint->sp_reg)) {
WARN_FUNC("unsupported unwind_hint sp base reg %d",
insn->sec, insn->offset, hint->sp_reg);
return -1;
}

- cfa->offset = hint->sp_offset;
+ insn->cfi.cfa.offset = hint->sp_offset;
insn->cfi.type = hint->type;
insn->cfi.end = hint->end;
}
@@ -1742,27 +1747,18 @@ static bool is_fentry_call(struct instru

static bool has_modified_stack_frame(struct instruction *insn, struct insn_state *state)
{
- u8 ret_offset = insn->ret_offset;
struct cfi_state *cfi = &state->cfi;
int i;

if (cfi->cfa.base != initial_func_cfi.cfa.base || cfi->drap)
return true;

- if (cfi->cfa.offset != initial_func_cfi.cfa.offset + ret_offset)
+ if (cfi->cfa.offset != initial_func_cfi.cfa.offset)
return true;

- if (cfi->stack_size != initial_func_cfi.cfa.offset + ret_offset)
+ if (cfi->stack_size != initial_func_cfi.cfa.offset)
return true;

- /*
- * If there is a ret offset hint then don't check registers
- * because a callee-saved register might have been pushed on
- * the stack.
- */
- if (ret_offset)
- return false;
-
for (i = 0; i < CFI_NUM_REGS; i++) {
if (cfi->regs[i].base != initial_func_cfi.regs[i].base ||
cfi->regs[i].offset != initial_func_cfi.regs[i].offset)
@@ -2863,10 +2859,7 @@ static int validate_section(struct objto
continue;

init_insn_state(&state, sec);
- state.cfi.cfa = initial_func_cfi.cfa;
- memcpy(&state.cfi.regs, &initial_func_cfi.regs,
- CFI_NUM_REGS * sizeof(struct cfi_reg));
- state.cfi.stack_size = initial_func_cfi.cfa.offset;
+ set_func_state(&state.cfi);

warnings += validate_symbol(file, sec, func, &state);
}
--- a/tools/objtool/check.h
+++ b/tools/objtool/check.h
@@ -50,7 +50,6 @@ struct instruction {
bool retpoline_safe;
s8 instr;
u8 visited;
- u8 ret_offset;
struct alt_group *alt_group;
struct symbol *call_dest;
struct instruction *jump_dest;