lkml.org 
[lkml]   [2021]   [Oct]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: [PATCH 4/9] x86/alternative: Implement .retpoline_sites support
On Wed, Oct 13, 2021 at 01:52:59PM -0700, Josh Poimboeuf wrote:

> BTW, CALL_NOSPEC results in a retpoline site in .altinstr_replacement:
>
> Relocation section [40] '.rela.retpoline_sites' for section [39] '.retpoline_sites' at offset 0x8d28 contains 1 entry:
> Offset Type Value Addend Name
> 000000000000000000 X86_64_PC32 000000000000000000 +10 .altinstr_replacement
>
> Which I assume we don't want.

(I missed this initially, and just independently rediscovered it)

In principle this problem affects static_call_list, the __sanitizer_cov_
and __fentry__ and now retpoline_sites.

Granted, it seems really unlikely to find __fentry__ or __sanitizer_cov_
references in alternatives, but it should be trivial to manually create
one.

I'm thinking we want to exclude all those when found in
.altinstr_replacement, right? It just doesn't make sense to rewrite
replacement text.

How is something like the below? (I'm not completely happy with it, but
I couldn't think of something better either).

---
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1039,14 +1039,39 @@ static void remove_insn_ops(struct instr
}
}

+#define DEST_RETPOLINE ((void *)-1L)
+
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)
+ if (dest != DEST_RETPOLINE) {
+ insn->call_dest = dest;
+ if (!dest )
+ return;
+ }
+
+ /*
+ * 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);
+
+ /*
+ * Whatever we do, do not rewrite replacement text.
+ */
+ if (!strcmp(insn->sec->name, ".altinstr_replacement"))
+ return;
+
+ if (dest == DEST_RETPOLINE) {
+ list_add_tail(&insn->call_node,
+ &file->retpoline_call_list);
return;
+ }

if (insn->call_dest->static_call_tramp) {
list_add_tail(&insn->call_node,
@@ -1091,15 +1116,6 @@ static void add_call_dest(struct objtool
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);
}

/*
@@ -1133,10 +1149,9 @@ static int add_jump_destinations(struct
else
insn->type = INSN_JUMP_DYNAMIC_CONDITIONAL;

- list_add_tail(&insn->call_node,
- &file->retpoline_call_list);
-
insn->retpoline_safe = true;
+
+ add_call_dest(file, insn, DEST_RETPOLINE, true);
continue;
} else if (insn->func) {
/* internal or external sibling call (with reloc) */
@@ -1272,12 +1287,7 @@ static int add_call_destinations(struct
insn->type = INSN_CALL_DYNAMIC;
insn->retpoline_safe = true;

- list_add_tail(&insn->call_node,
- &file->retpoline_call_list);
-
- remove_insn_ops(insn);
- continue;
-
+ add_call_dest(file, insn, DEST_RETPOLINE, false);
} else
add_call_dest(file, insn, reloc->sym, false);
}
\
 
 \ /
  Last update: 2021-10-19 13:37    [W:5.014 / U:0.120 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site