Messages in this thread Patch in this message | | | Date | Thu, 12 Mar 2020 23:23:24 +0100 | From | Peter Zijlstra <> | Subject | Re: [RFC][PATCH 00/16] objtool: vmlinux.o and noinstr validation |
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On Thu, Mar 12, 2020 at 05:23:37PM +0100, Peter Zijlstra wrote:
> So one of the problem i've ran into while playing with this and Thomas' > patches is that it is 'difficult' to deal with indirect function calls. > > objtool basically gives up instantly. > > I know smatch has passes were it looks for function pointer assignments > and carries that forward into it's callchain generation. Doing something > like that for objtool is going to be 'fun'... > > For now I've got limited success dodging a few instances with > __always_inline (which then results in the compiler resolving the > indirection).
Here's a little something that at least detects 'immediate' function pointers crossing the boundary.
It's slow though; it almost tripples the runtime. But I'm too tired to make it fast, maybe tomorrow.
---
--- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -247,6 +247,9 @@ static int decode_instructions(struct ob strncmp(sec->name, ".discard.", 9)) sec->text = true;
+ if (!strcmp(sec->name, ".noinstr.text")) + sec->noinstr = true; + for (offset = 0; offset < sec->len; offset += insn->len) { insn = malloc(sizeof(*insn)); if (!insn) { @@ -2040,6 +2043,28 @@ static int validate_return(struct symbol return 0; }
+static int validate_rela(struct instruction *insn, struct insn_state *state) +{ + struct section *sec; + struct rela *rela; + + if (!(state->noinstr && state->instr <= 0)) + return 0; + + rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len); + if (!rela || !rela->sym || !rela->sym->sec) + return 0; + + sec = rela->sym->sec; + if (sec->text && !sec->noinstr) { + WARN_FUNC("loading non-noinstr function pointer\n", + insn->sec, insn->offset); + return 1; + } + + return 0; +} + /* * Follow the branch starting at the given instruction, and recursively follow * any other branches (jumps). Meanwhile, track the frame pointer state at @@ -2222,6 +2247,10 @@ static int validate_branch(struct objtoo return 0;
case INSN_STACK: + ret = validate_rela(insn, &state); + if (ret) + return ret; + if (update_insn_state(insn, &state)) return 1;
@@ -2285,6 +2314,10 @@ static int validate_branch(struct objtoo break;
default: + ret = validate_rela(insn, &state); + if (ret) + return ret; + break; }
@@ -2442,8 +2475,8 @@ static int validate_sec_functions(struct * not correctly determine insn->call_dest->sec (external symbols do * not have a section). */ - if (vmlinux && !strcmp(sec->name, ".noinstr.text")) - state.noinstr = true; + if (vmlinux) + state.noinstr = sec->noinstr;
list_for_each_entry(func, &sec->symbol_list, list) { if (func->type != STT_FUNC) --- a/tools/objtool/elf.h +++ b/tools/objtool/elf.h @@ -43,7 +43,7 @@ struct section { char *name; int idx; unsigned int len; - bool changed, text, rodata; + bool changed, text, rodata, noinstr; };
struct symbol {
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