objtool: Fix noinstr vs KCOV

Since many compilers cannot disable KCOV with a function attribute,
help it to NOP out any __sanitizer_cov_*() calls injected in noinstr
code.

This turns:

12:   e8 00 00 00 00          callq  17 <lockdep_hardirqs_on+0x17>
		13: R_X86_64_PLT32      __sanitizer_cov_trace_pc-0x4

into:

12:   0f 1f 44 00 00          nopl   0x0(%rax,%rax,1)
		13: R_X86_64_NONE      __sanitizer_cov_trace_pc-0x4

Just like recordmcount does.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Dmitry Vyukov <dvyukov@google.com>

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 6a0cc524882dbee2a277eb7e88700968344d5728..883da0abf7790c3ef8b01fe0e39688a4531cd5ac 100644 (file)
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -67,7 +67,7 @@ config X86
        select ARCH_HAS_FILTER_PGPROT
        select ARCH_HAS_FORTIFY_SOURCE
        select ARCH_HAS_GCOV_PROFILE_ALL
-       select ARCH_HAS_KCOV                    if X86_64
+       select ARCH_HAS_KCOV                    if X86_64 && STACK_VALIDATION
        select ARCH_HAS_MEM_ENCRYPT
        select ARCH_HAS_MEMBARRIER_SYNC_CORE
        select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE

diff --git a/tools/objtool/arch.h b/tools/objtool/arch.h
index eda15a5a285e9224f554ff9fa91678ca888eaf85..3c5967748abb93917cc43f5841084d0fd5ce87f1 100644 (file)
--- a/tools/objtool/arch.h
+++ b/tools/objtool/arch.h
@@ -84,4 +84,6 @@ unsigned long arch_jump_destination(struct instruction *insn);
 
 unsigned long arch_dest_rela_offset(int addend);
 
+const char *arch_nop_insn(int len);
+
 #endif /* _ARCH_H */

diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c
index 4b504fc90bbb37a50dcb63f103c7214498fd56c4..9872195f998b023198862a9d67f04e0b20efdf64 100644 (file)
--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -565,3 +565,21 @@ void arch_initial_func_cfi_state(struct cfi_init_state *state)
        state->regs[16].base = CFI_CFA;
        state->regs[16].offset = -8;
 }
+
+const char *arch_nop_insn(int len)
+{
+       static const char nops[5][5] = {
+               /* 1 */ { 0x90 },
+               /* 2 */ { 0x66, 0x90 },
+               /* 3 */ { 0x0f, 0x1f, 0x00 },
+               /* 4 */ { 0x0f, 0x1f, 0x40, 0x00 },
+               /* 5 */ { 0x0f, 0x1f, 0x44, 0x00, 0x00 },
+       };
+
+       if (len < 1 || len > 5) {
+               WARN("invalid NOP size: %d\n", len);
+               return NULL;
+       }
+
+       return nops[len-1];
+}

diff --git a/tools/objtool/arch/x86/include/arch_elf.h b/tools/objtool/arch/x86/include/arch_elf.h
new file mode 100644 (file)
index 0000000..69cc426
--- /dev/null
+++ b/tools/objtool/arch/x86/include/arch_elf.h
@@ -0,0 +1,6 @@
+#ifndef _OBJTOOL_ARCH_ELF
+#define _OBJTOOL_ARCH_ELF
+
+#define R_NONE R_X86_64_NONE
+
+#endif /* _OBJTOOL_ARCH_ELF */

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 91a67db261650ee175fcb4a21365fedbc86d97ee..478267a072d08056d3f9c46a3305f1d743017d54 100644 (file)
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -12,6 +12,7 @@
 #include "check.h"
 #include "special.h"
 #include "warn.h"
+#include "arch_elf.h"
 
 #include <linux/hashtable.h>
 #include <linux/kernel.h>
@@ -765,6 +766,24 @@ static int add_call_destinations(struct objtool_file *file)
                } else
                        insn->call_dest = rela->sym;
 
+               /*
+                * Many compilers cannot disable KCOV with a function attribute
+                * so they need a little help, NOP out any KCOV calls from noinstr
+                * text.
+                */
+               if (insn->sec->noinstr &&
+                   !strncmp(insn->call_dest->name, "__sanitizer_cov_", 16)) {
+                       if (rela) {
+                               rela->type = R_NONE;
+                               elf_write_rela(file->elf, rela);
+                       }
+
+                       elf_write_insn(file->elf, insn->sec,
+                                      insn->offset, insn->len,
+                                      arch_nop_insn(insn->len));
+                       insn->type = INSN_NOP;
+               }
+
                /*
                 * Whatever stack impact regular CALLs have, should be undone
                 * by the RETURN of the called function.