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objtool: Introduce HINT_RET_OFFSET 

Normally objtool ensures a function keeps the stack layout invariant.
But there is a useful exception, it is possible to stuff the return
stack in order to 'inject' a 'call':

	push $fun
	ret

In this case the invariant mentioned above is violated.

Add an objtool HINT to annotate this and allow a function exit with a
modified stack frame.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lkml.kernel.org/r/20200416115118.690601403@infradead.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra 2020-04-01 16:38:19 +02:00 committed by Ingo Molnar
parent b746046238
commit e25eea89bb
5 changed files with 31 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
arch/x86/include/asm/orc_types.h
View File

@ -60,6 +60,7 @@
#define ORC_TYPE_REGS_IRET 2
#define UNWIND_HINT_TYPE_SAVE 3
#define UNWIND_HINT_TYPE_RESTORE 4
#define UNWIND_HINT_TYPE_RET_OFFSET 5
#ifndef __ASSEMBLY__
/*

10
arch/x86/include/asm/unwind_hints.h
View File

@ -94,6 +94,16 @@
UNWIND_HINT type=UNWIND_HINT_TYPE_RESTORE
.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 type=UNWIND_HINT_TYPE_RET_OFFSET sp_offset=\sp_offset
.endm
#else /* !__ASSEMBLY__ */
#define UNWIND_HINT(sp_reg, sp_offset, type, end) \

1
tools/arch/x86/include/asm/orc_types.h
View File

@ -60,6 +60,7 @@
#define ORC_TYPE_REGS_IRET 2
#define UNWIND_HINT_TYPE_SAVE 3
#define UNWIND_HINT_TYPE_RESTORE 4
#define UNWIND_HINT_TYPE_RET_OFFSET 5
#ifndef __ASSEMBLY__
/*

24
tools/objtool/check.c
View File

@ -1261,6 +1261,9 @@ static int read_unwind_hints(struct objtool_file *file)
} else if (hint->type == UNWIND_HINT_TYPE_RESTORE) {
insn->restore = true;
insn->hint = true;
} else if (hint->type == UNWIND_HINT_TYPE_RET_OFFSET) {
insn->ret_offset = hint->sp_offset;
continue;
}
@ -1424,20 +1427,25 @@ static bool is_fentry_call(struct instruction *insn)
return false;
}
static bool has_modified_stack_frame(struct insn_state *state)
static bool has_modified_stack_frame(struct instruction *insn, struct insn_state *state)
{
u8 ret_offset = insn->ret_offset;
int i;
if (state->cfa.base != initial_func_cfi.cfa.base ||
state->cfa.offset != initial_func_cfi.cfa.offset ||
state->stack_size != initial_func_cfi.cfa.offset ||
state->drap)
if (state->cfa.base != initial_func_cfi.cfa.base || state->drap)
return true;
for (i = 0; i < CFI_NUM_REGS; i++)
if (state->cfa.offset != initial_func_cfi.cfa.offset + ret_offset)
return true;
if (state->stack_size != initial_func_cfi.cfa.offset + ret_offset)
return true;
for (i = 0; i < CFI_NUM_REGS; i++) {
if (state->regs[i].base != initial_func_cfi.regs[i].base ||
state->regs[i].offset != initial_func_cfi.regs[i].offset)
return true;
}
return false;
}
@ -2014,7 +2022,7 @@ static int validate_call(struct instruction *insn, struct insn_state *state)
static int validate_sibling_call(struct instruction *insn, struct insn_state *state)
{
if (has_modified_stack_frame(state)) {
if (has_modified_stack_frame(insn, state)) {
WARN_FUNC("sibling call from callable instruction with modified stack frame",
insn->sec, insn->offset);
return 1;
@ -2043,7 +2051,7 @@ static int validate_return(struct symbol *func, struct instruction *insn, struct
return 1;
}
if (func && has_modified_stack_frame(state)) {
if (func && has_modified_stack_frame(insn, state)) {
WARN_FUNC("return with modified stack frame",
insn->sec, insn->offset);
return 1;

4
tools/objtool/check.h
View File

@ -33,9 +33,11 @@ struct instruction {
unsigned int len;
enum insn_type type;
unsigned long immediate;
bool alt_group, dead_end, ignore, hint, save, restore, ignore_alts;
bool alt_group, dead_end, ignore, ignore_alts;
bool hint, save, restore;
bool retpoline_safe;
u8 visited;
u8 ret_offset;
struct symbol *call_dest;
struct instruction *jump_dest;
struct instruction *first_jump_src;