Re: [RFC][PATCH] objtool: STAC/CLAC validation
flat view
From: Peter Zijlstra <peterz@infradead.org>
Date: 2019-02-25 13:21:17
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On Mon, Feb 25, 2019 at 12:47:00AM -0800, hpa@zytor.com wrote:
It doesn't have to understand the contents of the memop, but it seems that the presence of a modrm with mode ≠ 3 should be plenty. It needs to know that much in order to know the length of instructions anyway. For extra credit, ignore LEA or hinting instructions.
A little something like so then? arch/x86/kernel/fpu/signal.o: warning: objtool: .altinstr_replacement+0x9c: UACCESS disable without MEMOPs: copy_fpstate_to_sigframe() 00000000023c 000200000002 R_X86_64_PC32 0000000000000000 .text + 604 000000000240 000700000002 R_X86_64_PC32 0000000000000000 .altinstr_replacement + 99 000000000249 000200000002 R_X86_64_PC32 0000000000000000 .text + 610 00000000024d 000700000002 R_X86_64_PC32 0000000000000000 .altinstr_replacement + 9c .text 604: 90 nop 605: 90 nop 606: 90 nop 607: 83 ce 03 or $0x3,%esi 60a: 89 b3 00 02 00 00 mov %esi,0x200(%rbx) 610: 90 nop 611: 90 nop 612: 90 nop .altinstr_replacement 99: 0f 01 cb stac 9c: 0f 01 ca clac Which looks like the tool failed to recognise that MOV as a memop. ---
--- a/tools/objtool/arch.h
+++ b/tools/objtool/arch.h@@ -37,7 +37,8 @@ #define INSN_CLAC 12 #define INSN_STD 13 #define INSN_CLD 14 -#define INSN_OTHER 15 +#define INSN_MEMOP 15 +#define INSN_OTHER 16 #define INSN_LAST INSN_OTHER enum op_dest_type { --- a/tools/objtool/arch/x86/decode.c +++ b/tools/objtool/arch/x86/decode.c
@@ -123,6 +123,9 @@ int arch_decode_instruction(struct elf * modrm_mod = X86_MODRM_MOD(modrm); modrm_reg = X86_MODRM_REG(modrm); modrm_rm = X86_MODRM_RM(modrm); + + if (modrm_mod != 3) + *type = INSN_MEMOP; } if (insn.sib.nbytes) --- a/tools/objtool/check.c +++ b/tools/objtool/check.c
@@ -2047,6 +2047,7 @@ static int validate_branch(struct objtoo WARN_FUNC("recursive UACCESS enable", sec, insn->offset); state.uaccess = true; + state.memop = false; break; case INSN_CLAC:
@@ -2058,6 +2059,9 @@ static int validate_branch(struct objtoo break; } + if (!state.memop && insn->func) + WARN_FUNC("UACCESS disable without MEMOPs: %s()", sec, insn->offset, insn->func->name); + state.uaccess = false; break;
@@ -2075,6 +2079,10 @@ static int validate_branch(struct objtoo state.df = false; break; + case INSN_MEMOP: + state.memop = true; + break; + default: break; } --- a/tools/objtool/check.h +++ b/tools/objtool/check.h
@@ -31,7 +31,7 @@ struct insn_state { int stack_size; unsigned char type; bool bp_scratch; - bool drap, end, uaccess, uaccess_safe, df; + bool drap, end, uaccess, uaccess_safe, df, memop; int drap_reg, drap_offset; struct cfi_reg vals[CFI_NUM_REGS]; };
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