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authorPeter Zijlstra <peterz@infradead.org>2021-03-26 16:12:15 +0100
committerIngo Molnar <mingo@kernel.org>2021-04-02 12:47:28 +0200
commit9bc0bb50727c8ac69fbb33fb937431cf3518ff37 (patch)
tree586a82e95847ae6c3f393728fb074b1d6df9ae71 /tools/objtool
parent50e7b4a1a1b264fc7df0698f2defb93cadf19a7b (diff)
objtool/x86: Rewrite retpoline thunk calls
When the compiler emits: "CALL __x86_indirect_thunk_\reg" for an indirect call, have objtool rewrite it to: ALTERNATIVE "call __x86_indirect_thunk_\reg", "call *%reg", ALT_NOT(X86_FEATURE_RETPOLINE) Additionally, in order to not emit endless identical .altinst_replacement chunks, use a global symbol for them, see __x86_indirect_alt_*. This also avoids objtool from having to do code generation. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Borislav Petkov <bp@suse.de> Signed-off-by: Ingo Molnar <mingo@kernel.org> Reviewed-by: Miroslav Benes <mbenes@suse.cz> Link: https://lkml.kernel.org/r/20210326151300.320177914@infradead.org
Diffstat (limited to 'tools/objtool')
-rw-r--r--tools/objtool/arch/x86/decode.c117
1 files changed, 117 insertions, 0 deletions
diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c
index 782894eb351a..7e8b5bedd946 100644
--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -19,6 +19,7 @@
#include <objtool/elf.h>
#include <objtool/arch.h>
#include <objtool/warn.h>
+#include <arch/elf.h>
static unsigned char op_to_cfi_reg[][2] = {
{CFI_AX, CFI_R8},
@@ -613,6 +614,122 @@ const char *arch_nop_insn(int len)
return nops[len-1];
}
+/* asm/alternative.h ? */
+
+#define ALTINSTR_FLAG_INV (1 << 15)
+#define ALT_NOT(feat) ((feat) | ALTINSTR_FLAG_INV)
+
+struct alt_instr {
+ s32 instr_offset; /* original instruction */
+ s32 repl_offset; /* offset to replacement instruction */
+ u16 cpuid; /* cpuid bit set for replacement */
+ u8 instrlen; /* length of original instruction */
+ u8 replacementlen; /* length of new instruction */
+} __packed;
+
+static int elf_add_alternative(struct elf *elf,
+ struct instruction *orig, struct symbol *sym,
+ int cpuid, u8 orig_len, u8 repl_len)
+{
+ const int size = sizeof(struct alt_instr);
+ struct alt_instr *alt;
+ struct section *sec;
+ Elf_Scn *s;
+
+ sec = find_section_by_name(elf, ".altinstructions");
+ if (!sec) {
+ sec = elf_create_section(elf, ".altinstructions",
+ SHF_WRITE, size, 0);
+
+ if (!sec) {
+ WARN_ELF("elf_create_section");
+ return -1;
+ }
+ }
+
+ s = elf_getscn(elf->elf, sec->idx);
+ if (!s) {
+ WARN_ELF("elf_getscn");
+ return -1;
+ }
+
+ sec->data = elf_newdata(s);
+ if (!sec->data) {
+ WARN_ELF("elf_newdata");
+ return -1;
+ }
+
+ sec->data->d_size = size;
+ sec->data->d_align = 1;
+
+ alt = sec->data->d_buf = malloc(size);
+ if (!sec->data->d_buf) {
+ perror("malloc");
+ return -1;
+ }
+ memset(sec->data->d_buf, 0, size);
+
+ if (elf_add_reloc_to_insn(elf, sec, sec->sh.sh_size,
+ R_X86_64_PC32, orig->sec, orig->offset)) {
+ WARN("elf_create_reloc: alt_instr::instr_offset");
+ return -1;
+ }
+
+ if (elf_add_reloc(elf, sec, sec->sh.sh_size + 4,
+ R_X86_64_PC32, sym, 0)) {
+ WARN("elf_create_reloc: alt_instr::repl_offset");
+ return -1;
+ }
+
+ alt->cpuid = cpuid;
+ alt->instrlen = orig_len;
+ alt->replacementlen = repl_len;
+
+ sec->sh.sh_size += size;
+ sec->changed = true;
+
+ return 0;
+}
+
+#define X86_FEATURE_RETPOLINE ( 7*32+12)
+
+int arch_rewrite_retpolines(struct objtool_file *file)
+{
+ struct instruction *insn;
+ struct reloc *reloc;
+ struct symbol *sym;
+ char name[32] = "";
+
+ list_for_each_entry(insn, &file->retpoline_call_list, call_node) {
+
+ if (!strcmp(insn->sec->name, ".text.__x86.indirect_thunk"))
+ continue;
+
+ reloc = insn->reloc;
+
+ sprintf(name, "__x86_indirect_alt_%s_%s",
+ insn->type == INSN_JUMP_DYNAMIC ? "jmp" : "call",
+ reloc->sym->name + 21);
+
+ sym = find_symbol_by_name(file->elf, name);
+ if (!sym) {
+ sym = elf_create_undef_symbol(file->elf, name);
+ if (!sym) {
+ WARN("elf_create_undef_symbol");
+ return -1;
+ }
+ }
+
+ if (elf_add_alternative(file->elf, insn, sym,
+ ALT_NOT(X86_FEATURE_RETPOLINE), 5, 5)) {
+ WARN("elf_add_alternative");
+ return -1;
+ }
+ }
+
+ return 0;
+}
+
int arch_decode_hint_reg(struct instruction *insn, u8 sp_reg)
{
struct cfi_reg *cfa = &insn->cfi.cfa;