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Date: Tue, 15 Jan 2019 14:45:22 -0800
From: Kees Cook <keescook@...omium.org>
To: Ruslan Nikolaev <nruslan_devel@...oo.com>
Cc: Kernel Hardening <kernel-hardening@...ts.openwall.com>,
Thomas Garnier <thgarnie@...gle.com>, X86 ML <x86@...nel.org>,
Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH v1 01/06]: Extending objtool for PIC modules
On Tue, Jan 15, 2019 at 10:56 AM Ruslan Nikolaev
<nruslan_devel@...oo.com> wrote:
>
> Extending objtool for PIC modules
>
> The patch is by Hassan Nadeem and Ruslan Nikolaev. This extends
> the prior PIE kernel patch (by Thomas Garnier) to also support
> position-independent modules that can be placed anywhere in the
> 48/64-bit address space (for better KASLR).
>
> Signed-off-by: Ruslan Nikolaev <nruslan_devel@...oo.com>
Thanks for working on this!
In the next version, you probably want to add the "Co-developed-by:"
and "Signed-off-by:" tags from Hassan Nadeem, as appropriate. Also,
I'd CC Josh Poimboeuf <jpoimboe@...hat.com> too, since he will likely
have comments on these improvements. :)
Once Thomas posts his next revision, I'll put together a tree with
both sets of patches so people can more easily test the combined
results.
-Kees
> ---
> check.c | 39 ++++++++++++++++++++++++++++-----------
> 1 file changed, 28 insertions(+), 11 deletions(-)
>
> diff -uprN a/tools/objtool/check.c b/tools/objtool/check.c
> --- a/tools/objtool/check.c 2019-01-15 11:20:46.047176216 -0500
> +++ b/tools/objtool/check.c 2019-01-15 11:20:57.727294197 -0500
> @@ -179,7 +179,7 @@ static int __dead_end_function(struct ob
> return 0;
>
> insn = find_insn(file, func->sec, func->offset);
> - if (!insn->func)
> + if (!insn || !insn->func)
> return 0;
>
> func_for_each_insn_all(file, func, insn) {
> @@ -233,6 +233,8 @@ static int __dead_end_function(struct ob
>
> static int dead_end_function(struct objtool_file *file, struct symbol
> *func)
> {
> + if (!func)
> + return 0;
> return __dead_end_function(file, func, 0);
> }
>
> @@ -581,7 +583,7 @@ static int add_call_destinations(struct
> struct rela *rela;
>
> for_each_insn(file, insn) {
> - if (insn->type != INSN_CALL)
> + if (insn->type != INSN_CALL && insn->type != INSN_CALL_DYNAMIC)
> continue;
>
> rela = find_rela_by_dest_range(insn->sec, insn->offset,
> @@ -590,8 +592,8 @@ static int add_call_destinations(struct
> dest_off = insn->offset + insn->len + insn->immediate;
> insn->call_dest = find_symbol_by_offset(insn->sec,
> dest_off);
> -
> - if (!insn->call_dest && !insn->ignore) {
> + if (!insn->call_dest && !insn->ignore &&
> + insn->type != INSN_CALL_DYNAMIC) {
> WARN_FUNC("unsupported intra-function call",
> insn->sec, insn->offset);
> if (retpoline)
> @@ -602,8 +604,9 @@ static int add_call_destinations(struct
> } else if (rela->sym->type == STT_SECTION) {
> insn->call_dest = find_symbol_by_offset(rela->sym->sec,
> rela->addend+4);
> - if (!insn->call_dest ||
> - insn->call_dest->type != STT_FUNC) {
> + if ((!insn->call_dest ||
> + insn->call_dest->type != STT_FUNC) &&
> + insn->type != INSN_CALL_DYNAMIC) {
> WARN_FUNC("can't find call dest symbol at %s+0x%x",
> insn->sec, insn->offset,
> rela->sym->sec->name,
> @@ -836,6 +839,11 @@ static int add_switch_table(struct objto
> struct symbol *pfunc = insn->func->pfunc;
> unsigned int prev_offset = 0;
>
> + /* If PC32 relocations are used (as in PIC), the following logic
> + * can be broken in many ways.
> + */
> + if (file->ignore_unreachables)
> + return 0;
> list_for_each_entry_from(rela, &file->rodata->rela->rela_list, list) {
> if (rela == next_table)
> break;
> @@ -1244,7 +1252,7 @@ static int decode_sections(struct objtoo
>
> static bool is_fentry_call(struct instruction *insn)
> {
> - if (insn->type == INSN_CALL &&
> + if (insn->call_dest &&
> insn->call_dest->type == STT_NOTYPE &&
> !strcmp(insn->call_dest->name, "__fentry__"))
> return true;
> @@ -1889,6 +1897,7 @@ static int validate_branch(struct objtoo
> return 0;
>
> case INSN_CALL:
> + case INSN_CALL_DYNAMIC:
> if (is_fentry_call(insn))
> break;
>
> @@ -1898,8 +1907,6 @@ static int validate_branch(struct objtoo
> if (ret == -1)
> return 1;
>
> - /* fallthrough */
> - case INSN_CALL_DYNAMIC:
> if (!no_fp && func && !has_valid_stack_frame(&state)) {
> WARN_FUNC("call without frame pointer save/setup",
> sec, insn->offset);
> @@ -1929,12 +1936,15 @@ static int validate_branch(struct objtoo
> break;
>
> case INSN_JUMP_DYNAMIC:
> + /* XXX: Does not work properly with PIC code. */
> +#if 0
> if (func && list_empty(&insn->alts) &&
> has_modified_stack_frame(&state)) {
> WARN_FUNC("sibling call from callable instruction with modified
> stack frame",
> sec, insn->offset);
> return 1;
> }
> +#endif
>
> return 0;
>
> @@ -2015,6 +2025,11 @@ static int validate_retpoline(struct obj
> if (!strcmp(insn->sec->name, ".init.text") && !module)
> continue;
>
> + /* ignore ftrace calls in PIC code */
> + if (!insn->call_dest ||
> + !strcmp(insn->call_dest->name, "__fentry__"))
> + continue;
> +
> WARN_FUNC("indirect %s found in RETPOLINE build",
> insn->sec, insn->offset,
> insn->type == INSN_JUMP_DYNAMIC ? "jump" : "call");
> @@ -2027,13 +2042,15 @@ static int validate_retpoline(struct obj
>
> static bool is_kasan_insn(struct instruction *insn)
> {
> - return (insn->type == INSN_CALL &&
> + return ((insn->type == INSN_CALL || insn->type == INSN_CALL_DYNAMIC) &&
> + insn->call_dest &&
> !strcmp(insn->call_dest->name, "__asan_handle_no_return"));
> }
>
> static bool is_ubsan_insn(struct instruction *insn)
> {
> - return (insn->type == INSN_CALL &&
> + return ((insn->type == INSN_CALL || insn->type == INSN_CALL_DYNAMIC) &&
> + insn->call_dest &&
> !strcmp(insn->call_dest->name,
> "__ubsan_handle_builtin_unreachable"));
> }
--
Kees Cook
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