[tip: objtool/core] objtool: Handle __sanitize_cov*() tail calls

tip-bot2 for Peter Zijlstra
2021-09-15T15:50:15Z

The following commit has been merged into the objtool/core branch of tip:

Commit-ID: f56dae88a81fded66adf2bea9922d1d98d1da14f
Gitweb: https://git.kernel.org/tip/f56dae88a81fded66adf2bea9922d1d98d1da14f
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Thu, 24 Jun 2021 11:41:02 +02:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Wed, 15 Sep 2021 15:51:45 +02:00

objtool: Handle __sanitize_cov*() tail calls

Turns out the compilers also generate tail calls to __sanitize_cov*(),
make sure to also patch those out in noinstr code.

Fixes: 0f1441b44e82 ("objtool: Fix noinstr vs KCOV")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Marco Elver <elver@google.com>
Link: https://lore.kernel.org/r/20210624095147.818783799@infradead.org
---
tools/objtool/arch/x86/decode.c | 20 +++-
tools/objtool/check.c | 158 +++++++++++++-------------
tools/objtool/include/objtool/arch.h | 1 +-
3 files changed, 105 insertions(+), 74 deletions(-)

diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c
index 3435a32..340a3dc 100644
--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -659,6 +659,26 @@ const char *arch_nop_insn(int len)
return nops[len-1];
}

+#define BYTE_RET 0xC3
+
+const char *arch_ret_insn(int len)
+{
+ static const char ret[5][5] = {
+ { BYTE_RET },
+ { BYTE_RET, BYTES_NOP1 },
+ { BYTE_RET, BYTES_NOP2 },
+ { BYTE_RET, BYTES_NOP3 },
+ { BYTE_RET, BYTES_NOP4 },
+ };
+
+ if (len < 1 || len > 5) {
+ WARN("invalid RET size: %d\n", len);
+ return NULL;
+ }
+
+ return ret[len-1];
+}
+
/* asm/alternative.h ? */

#define ALTINSTR_FLAG_INV (1 << 15)
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index d9f3273..c6f206f 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -904,6 +904,79 @@ static struct reloc *insn_reloc(struct objtool_file *file, struct instruction *i
return insn->reloc;
}

+static void remove_insn_ops(struct instruction *insn)
+{
+ struct stack_op *op, *tmp;
+
+ list_for_each_entry_safe(op, tmp, &insn->stack_ops, list) {
+ list_del(&op->list);
+ free(op);
+ }
+}
+
+static void add_call_dest(struct objtool_file *file, struct instruction *insn,
+ struct symbol *dest, bool sibling)
+{
+ struct reloc *reloc = insn_reloc(file, insn);
+
+ insn->call_dest = dest;
+ if (!dest)
+ return;
+
+ if (insn->call_dest->static_call_tramp) {
+ list_add_tail(&insn->call_node,
+ &file->static_call_list);
+ }
+
+ /*
+ * Many compilers cannot disable KCOV with a function attribute
+ * so they need a little help, NOP out any KCOV calls from noinstr
+ * text.
+ */
+ if (insn->sec->noinstr &&
+ !strncmp(insn->call_dest->name, "__sanitizer_cov_", 16)) {
+ if (reloc) {
+ reloc->type = R_NONE;
+ elf_write_reloc(file->elf, reloc);
+ }
+
+ elf_write_insn(file->elf, insn->sec,
+ insn->offset, insn->len,
+ sibling ? arch_ret_insn(insn->len)
+ : arch_nop_insn(insn->len));
+
+ insn->type = sibling ? INSN_RETURN : INSN_NOP;
+ }
+
+ if (mcount && !strcmp(insn->call_dest->name, "__fentry__")) {
+ if (sibling)
+ WARN_FUNC("Tail call to __fentry__ !?!?", insn->sec, insn->offset);
+
+ if (reloc) {
+ reloc->type = R_NONE;
+ elf_write_reloc(file->elf, reloc);
+ }
+
+ elf_write_insn(file->elf, insn->sec,
+ insn->offset, insn->len,
+ arch_nop_insn(insn->len));
+
+ insn->type = INSN_NOP;
+
+ list_add_tail(&insn->mcount_loc_node,
+ &file->mcount_loc_list);
+ }
+
+ /*
+ * Whatever stack impact regular CALLs have, should be undone
+ * by the RETURN of the called function.
+ *
+ * Annotated intra-function calls retain the stack_ops but
+ * are converted to JUMP, see read_intra_function_calls().
+ */
+ remove_insn_ops(insn);
+}
+
/*
* Find the destination instructions for all jumps.
*/
@@ -942,11 +1015,7 @@ static int add_jump_destinations(struct objtool_file *file)
continue;
} else if (insn->func) {
/* internal or external sibling call (with reloc) */
- insn->call_dest = reloc->sym;
- if (insn->call_dest->static_call_tramp) {
- list_add_tail(&insn->call_node,
- &file->static_call_list);
- }
+ add_call_dest(file, insn, reloc->sym, true);
continue;
} else if (reloc->sym->sec->idx) {
dest_sec = reloc->sym->sec;
@@ -1002,13 +1071,8 @@ static int add_jump_destinations(struct objtool_file *file)

} else if (insn->jump_dest->func->pfunc != insn->func->pfunc &&
insn->jump_dest->offset == insn->jump_dest->func->offset) {
-
/* internal sibling call (without reloc) */
- insn->call_dest = insn->jump_dest->func;
- if (insn->call_dest->static_call_tramp) {
- list_add_tail(&insn->call_node,
- &file->static_call_list);
- }
+ add_call_dest(file, insn, insn->jump_dest->func, true);
}
}
}
@@ -1016,16 +1080,6 @@ static int add_jump_destinations(struct objtool_file *file)
return 0;
}

-static void remove_insn_ops(struct instruction *insn)
-{
- struct stack_op *op, *tmp;
-
- list_for_each_entry_safe(op, tmp, &insn->stack_ops, list) {
- list_del(&op->list);
- free(op);
- }
-}
-
static struct symbol *find_call_destination(struct section *sec, unsigned long offset)
{
struct symbol *call_dest;
@@ -1044,6 +1098,7 @@ static int add_call_destinations(struct objtool_file *file)
{
struct instruction *insn;
unsigned long dest_off;
+ struct symbol *dest;
struct reloc *reloc;

for_each_insn(file, insn) {
@@ -1053,7 +1108,9 @@ static int add_call_destinations(struct objtool_file *file)
reloc = insn_reloc(file, insn);
if (!reloc) {
dest_off = arch_jump_destination(insn);
- insn->call_dest = find_call_destination(insn->sec, dest_off);
+ dest = find_call_destination(insn->sec, dest_off);
+
+ add_call_dest(file, insn, dest, false);

if (insn->ignore)
continue;
@@ -1071,9 +1128,8 @@ static int add_call_destinations(struct objtool_file *file)

} else if (reloc->sym->type == STT_SECTION) {
dest_off = arch_dest_reloc_offset(reloc->addend);
- insn->call_dest = find_call_destination(reloc->sym->sec,
- dest_off);
- if (!insn->call_dest) {
+ dest = find_call_destination(reloc->sym->sec, dest_off);
+ if (!dest) {
WARN_FUNC("can't find call dest symbol at %s+0x%lx",
insn->sec, insn->offset,
reloc->sym->sec->name,
@@ -1081,6 +1137,8 @@ static int add_call_destinations(struct objtool_file *file)
return -1;
}

+ add_call_dest(file, insn, dest, false);
+
} else if (arch_is_retpoline(reloc->sym)) {
/*
* Retpoline calls are really dynamic calls in
@@ -1096,55 +1154,7 @@ static int add_call_destinations(struct objtool_file *file)
continue;

} else
- insn->call_dest = reloc->sym;
-
- if (insn->call_dest && insn->call_dest->static_call_tramp) {
- list_add_tail(&insn->call_node,
- &file->static_call_list);
- }
-
- /*
- * Many compilers cannot disable KCOV with a function attribute
- * so they need a little help, NOP out any KCOV calls from noinstr
- * text.
- */
- if (insn->sec->noinstr &&
- !strncmp(insn->call_dest->name, "__sanitizer_cov_", 16)) {
- if (reloc) {
- reloc->type = R_NONE;
- elf_write_reloc(file->elf, reloc);
- }
-
- elf_write_insn(file->elf, insn->sec,
- insn->offset, insn->len,
- arch_nop_insn(insn->len));
- insn->type = INSN_NOP;
- }
-
- if (mcount && !strcmp(insn->call_dest->name, "__fentry__")) {
- if (reloc) {
- reloc->type = R_NONE;
- elf_write_reloc(file->elf, reloc);
- }
-
- elf_write_insn(file->elf, insn->sec,
- insn->offset, insn->len,
- arch_nop_insn(insn->len));
-
- insn->type = INSN_NOP;
-
- list_add_tail(&insn->mcount_loc_node,
- &file->mcount_loc_list);
- }
-
- /*
- * Whatever stack impact regular CALLs have, should be undone
- * by the RETURN of the called function.
- *
- * Annotated intra-function calls retain the stack_ops but
- * are converted to JUMP, see read_intra_function_calls().
- */
- remove_insn_ops(insn);
+ add_call_dest(file, insn, reloc->sym, false);
}

return 0;
diff --git a/tools/objtool/include/objtool/arch.h b/tools/objtool/include/objtool/arch.h
index a5ab682..6f482ae 100644
--- a/tools/objtool/include/objtool/arch.h
+++ b/tools/objtool/include/objtool/arch.h
@@ -82,6 +82,7 @@ unsigned long arch_jump_destination(struct instruction *insn);
unsigned long arch_dest_reloc_offset(int addend);

const char *arch_nop_insn(int len);
+const char *arch_ret_insn(int len);

int arch_decode_hint_reg(u8 sp_reg, int *base);