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Message-Id: <3da23a6d4c5b3c1e21fc2ccc21a73941b97ff20a.1502401017.git.jpoimboe@redhat.com>
Date: Thu, 10 Aug 2017 16:37:26 -0500
From: Josh Poimboeuf <jpoimboe@...hat.com>
To: x86@...nel.org
Cc: linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...db.de>
Subject: [PATCH 2/2] objtool: Track DRAP separately from callee-saved registers
When GCC realigns a function's stack, it sometimes uses %r13 as the DRAP
register, like:
push %r13
lea 0x10(%rsp), %r13
and $0xfffffffffffffff0, %rsp
pushq -0x8(%r13)
push %rbp
mov %rsp, %rbp
push %r13
...
mov -0x8(%rbp),%r13
leaveq
lea -0x10(%r13), %rsp
pop %r13
retq
Since %r13 was pushed onto the stack twice, its two stack locations need
to be stored separately. The first push of %r13 is its original value,
and the second push of %r13 is the caller's stack frame address.
Since %r13 is a callee-saved register, we need to track the stack
location of its original value separately from the DRAP register.
This fixes the following false positive warning:
lib/ubsan.o: warning: objtool: val_to_string.constprop.7()+0x97: leave instruction with modified stack frame
Reported-by: Arnd Bergmann <arnd@...db.de>
Fixes: baa41469a7b9 ("objtool: Implement stack validation 2.0")
Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
---
tools/objtool/check.c | 54 ++++++++++++++++++++++++++++-----------------------
tools/objtool/check.h | 2 +-
2 files changed, 31 insertions(+), 25 deletions(-)
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 5814e907f8c2..17375925e7aa 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -221,6 +221,7 @@ static void clear_insn_state(struct insn_state *state)
for (i = 0; i < CFI_NUM_REGS; i++)
state->regs[i].base = CFI_UNDEFINED;
state->drap_reg = CFI_UNDEFINED;
+ state->drap_offset = -1;
}
/*
@@ -1110,8 +1111,7 @@ static int update_insn_state_regs(struct instruction *insn, struct insn_state *s
static void save_reg(struct insn_state *state, unsigned char reg, int base,
int offset)
{
- if ((arch_callee_saved_reg(reg) ||
- (state->drap && reg == state->drap_reg)) &&
+ if (arch_callee_saved_reg(reg) &&
state->regs[reg].base == CFI_UNDEFINED) {
state->regs[reg].base = base;
state->regs[reg].offset = offset;
@@ -1281,7 +1281,6 @@ static int update_insn_state(struct instruction *insn, struct insn_state *state)
cfa->base = state->drap_reg;
cfa->offset = state->stack_size = 0;
state->drap = true;
-
}
/*
@@ -1299,17 +1298,19 @@ static int update_insn_state(struct instruction *insn, struct insn_state *state)
cfa->base = CFI_SP;
}
- if (regs[op->dest.reg].offset == -state->stack_size) {
+ if (state->drap && cfa->base == CFI_BP_INDIRECT &&
+ op->dest.type == OP_DEST_REG &&
+ op->dest.reg == state->drap_reg &&
+ state->drap_offset == -state->stack_size) {
- if (state->drap && cfa->base == CFI_BP_INDIRECT &&
- op->dest.type == OP_DEST_REG &&
- op->dest.reg == state->drap_reg) {
+ /* drap: pop %drap */
+ cfa->base = state->drap_reg;
+ cfa->offset = 0;
+ state->drap_offset = -1;
- /* drap: pop %drap */
- cfa->base = state->drap_reg;
- cfa->offset = 0;
- }
+ } else if (regs[op->dest.reg].offset == -state->stack_size) {
+ /* pop %reg */
restore_reg(state, op->dest.reg);
}
@@ -1321,14 +1322,18 @@ static int update_insn_state(struct instruction *insn, struct insn_state *state)
case OP_SRC_REG_INDIRECT:
if (state->drap && op->src.reg == CFI_BP &&
+ op->src.offset == state->drap_offset) {
+
+ /* drap: mov disp(%rbp), %drap */
+ cfa->base = state->drap_reg;
+ cfa->offset = 0;
+ state->drap_offset = -1;
+ }
+
+ if (state->drap && op->src.reg == CFI_BP &&
op->src.offset == regs[op->dest.reg].offset) {
/* drap: mov disp(%rbp), %reg */
- if (op->dest.reg == state->drap_reg) {
- cfa->base = state->drap_reg;
- cfa->offset = 0;
- }
-
restore_reg(state, op->dest.reg);
} else if (op->src.reg == cfa->base &&
@@ -1364,8 +1369,8 @@ static int update_insn_state(struct instruction *insn, struct insn_state *state)
cfa->base = CFI_BP_INDIRECT;
cfa->offset = -state->stack_size;
- /* save drap so we know when to undefine it */
- save_reg(state, op->src.reg, CFI_CFA, -state->stack_size);
+ /* save drap so we know when to restore it */
+ state->drap_offset = -state->stack_size;
} else if (op->src.reg == CFI_BP && cfa->base == state->drap_reg) {
@@ -1399,8 +1404,8 @@ static int update_insn_state(struct instruction *insn, struct insn_state *state)
cfa->base = CFI_BP_INDIRECT;
cfa->offset = op->dest.offset;
- /* save drap so we know when to undefine it */
- save_reg(state, op->src.reg, CFI_CFA, op->dest.offset);
+ /* save drap offset so we know when to restore it */
+ state->drap_offset = op->dest.offset;
}
else if (regs[op->src.reg].base == CFI_UNDEFINED) {
@@ -1491,11 +1496,12 @@ static bool insn_state_match(struct instruction *insn, struct insn_state *state)
insn->sec, insn->offset, state1->type, state2->type);
} else if (state1->drap != state2->drap ||
- (state1->drap && state1->drap_reg != state2->drap_reg)) {
- WARN_FUNC("stack state mismatch: drap1=%d(%d) drap2=%d(%d)",
+ (state1->drap && state1->drap_reg != state2->drap_reg) ||
+ (state1->drap && state1->drap_offset != state2->drap_offset)) {
+ WARN_FUNC("stack state mismatch: drap1=%d(%d,%d) drap2=%d(%d,%d)",
insn->sec, insn->offset,
- state1->drap, state1->drap_reg,
- state2->drap, state2->drap_reg);
+ state1->drap, state1->drap_reg, state1->drap_offset,
+ state2->drap, state2->drap_reg, state2->drap_offset);
} else
return true;
diff --git a/tools/objtool/check.h b/tools/objtool/check.h
index c9af11f0c8af..9f113016bf8c 100644
--- a/tools/objtool/check.h
+++ b/tools/objtool/check.h
@@ -32,7 +32,7 @@ struct insn_state {
unsigned char type;
bool bp_scratch;
bool drap;
- int drap_reg;
+ int drap_reg, drap_offset;
};
struct instruction {
--
2.13.3
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