From bf4d1a83758368c842c94cab9661a75ca98bc848 Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf Date: Thu, 10 Aug 2017 16:37:26 -0500 Subject: 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 Signed-off-by: Josh Poimboeuf Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Fixes: baa41469a7b9 ("objtool: Implement stack validation 2.0") Link: http://lkml.kernel.org/r/3da23a6d4c5b3c1e21fc2ccc21a73941b97ff20a.1502401017.git.jpoimboe@redhat.com Signed-off-by: Ingo Molnar --- tools/objtool/check.c | 54 ++++++++++++++++++++++++++++----------------------- tools/objtool/check.h | 2 +- 2 files changed, 31 insertions(+), 25 deletions(-) (limited to 'tools/objtool') 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); } @@ -1320,15 +1321,19 @@ static int update_insn_state(struct instruction *insn, struct insn_state *state) break; 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 { -- cgit