objtool: Combine UNWIND_HINT_RET_OFFSET and UNWIND_HINT_FUNC

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

diff --git a/arch/x86/include/asm/unwind_hints.h b/arch/x86/include/asm/unwind_hints.h
index 664d461..8e574c0 100644 (file)
--- 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__ */

diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S
index 58d125e..1bf568d 100644 (file)
--- a/arch/x86/kernel/ftrace_64.S
+++ b/arch/x86/kernel/ftrace_64.S
@@ -277,7 +277,7 @@ SYM_INNER_LABEL(ftrace_regs_caller_end, SYM_L_GLOBAL)
        restore_mcount_regs 8
        /* Restore flags */
        popfq
-       UNWIND_HINT_RET_OFFSET
+       UNWIND_HINT_FUNC
        jmp     ftrace_epilogue
 
 SYM_FUNC_END(ftrace_regs_caller)

diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S
index b4c43a9..f6fb1d2 100644 (file)
--- a/arch/x86/lib/retpoline.S
+++ b/arch/x86/lib/retpoline.S
@@ -28,7 +28,7 @@ SYM_FUNC_START_NOALIGN(__x86_retpoline_\reg)
        jmp     .Lspec_trap_\@
 .Ldo_rop_\@:
        mov     %\reg, (%_ASM_SP)
-       UNWIND_HINT_RET_OFFSET
+       UNWIND_HINT_FUNC
        ret
 SYM_FUNC_END(__x86_retpoline_\reg)
 

diff --git a/include/linux/objtool.h b/include/linux/objtool.h
index add1c6e..7e72d97 100644 (file)
--- 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
 

diff --git a/tools/include/linux/objtool.h b/tools/include/linux/objtool.h
index add1c6e..7e72d97 100644 (file)
--- 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
 

diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c
index 6baa227..9637e3b 100644 (file)
--- 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 cfi_init_state *state)
        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)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index b4e1655..f88f203 100644 (file)
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1404,13 +1404,20 @@ static int add_jump_table_alts(struct objtool_file *file)
        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");
@@ -1445,22 +1452,20 @@ static int read_unwind_hints(struct objtool_file *file)
                        return -1;
                }
 
-               cfa = &insn->cfi.cfa;
+               insn->hint = true;
 
-               if (hint->type == UNWIND_HINT_TYPE_RET_OFFSET) {
-                       insn->ret_offset = bswap_if_needed(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 = bswap_if_needed(hint->sp_offset);
+               insn->cfi.cfa.offset = bswap_if_needed(hint->sp_offset);
                insn->cfi.type = hint->type;
                insn->cfi.end = hint->end;
        }
@@ -1716,27 +1721,18 @@ static bool is_fentry_call(struct instruction *insn)
 
 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)
@@ -2880,10 +2876,7 @@ static int validate_section(struct objtool_file *file, struct section *sec)
                        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);
        }

diff --git a/tools/objtool/include/objtool/check.h b/tools/objtool/include/objtool/check.h
index b408636..4891ead 100644 (file)
--- a/tools/objtool/include/objtool/check.h
+++ b/tools/objtool/include/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;