From bd98c81346468fc2f86aeeb44d4d0d6f763a62b7 Mon Sep 17 00:00:00 2001 From: Jann Horn Date: Wed, 17 Jul 2019 20:36:54 -0500 Subject: objtool: Support repeated uses of the same C jump table This fixes objtool for both a GCC issue and a Clang issue: 1) GCC issue: kernel/bpf/core.o: warning: objtool: ___bpf_prog_run()+0x8d5: sibling call from callable instruction with modified stack frame With CONFIG_RETPOLINE=n, GCC is doing the following optimization in ___bpf_prog_run(). Before: select_insn: jmp *jumptable(,%rax,8) ... ALU64_ADD_X: ... jmp select_insn ALU_ADD_X: ... jmp select_insn After: select_insn: jmp *jumptable(, %rax, 8) ... ALU64_ADD_X: ... jmp *jumptable(, %rax, 8) ALU_ADD_X: ... jmp *jumptable(, %rax, 8) This confuses objtool. It has never seen multiple indirect jump sites which use the same jump table. For GCC switch tables, the only way of detecting the size of a table is by continuing to scan for more tables. The size of the previous table can only be determined after another switch table is found, or when the scan reaches the end of the function. That logic was reused for C jump tables, and was based on the assumption that each jump table only has a single jump site. The above optimization breaks that assumption. 2) Clang issue: drivers/usb/misc/sisusbvga/sisusb.o: warning: objtool: sisusb_write_mem_bulk()+0x588: can't find switch jump table With clang 9, code can be generated where a function contains two indirect jump instructions which use the same switch table. The fix is the same for both issues: split the jump table parsing into two passes. In the first pass, locate the heads of all switch tables for the function and mark their locations. In the second pass, parse the switch tables and add them. Fixes: e55a73251da3 ("bpf: Fix ORC unwinding in non-JIT BPF code") Reported-by: Randy Dunlap Reported-by: Arnd Bergmann Signed-off-by: Jann Horn Signed-off-by: Josh Poimboeuf Signed-off-by: Thomas Gleixner Tested-by: Nick Desaulniers Acked-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/e995befaada9d4d8b2cf788ff3f566ba900d2b4d.1563413318.git.jpoimboe@redhat.com Co-developed-by: Josh Poimboeuf --- tools/objtool/check.c | 53 +++++++++++++++++++++++++++------------------------ tools/objtool/check.h | 1 + tools/objtool/elf.h | 1 + 3 files changed, 30 insertions(+), 25 deletions(-) diff --git a/tools/objtool/check.c b/tools/objtool/check.c index 4525cf677a1b..66f7c01385a4 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -900,7 +900,7 @@ out: } static int add_jump_table(struct objtool_file *file, struct instruction *insn, - struct rela *table, struct rela *next_table) + struct rela *table) { struct rela *rela = table; struct instruction *dest_insn; @@ -913,7 +913,9 @@ static int add_jump_table(struct objtool_file *file, struct instruction *insn, * instruction. */ list_for_each_entry_from(rela, &table->sec->rela_list, list) { - if (rela == next_table) + + /* Check for the end of the table: */ + if (rela != table && rela->jump_table_start) break; /* Make sure the table entries are consecutive: */ @@ -1072,13 +1074,15 @@ static struct rela *find_jump_table(struct objtool_file *file, return NULL; } - -static int add_func_jump_tables(struct objtool_file *file, - struct symbol *func) +/* + * First pass: Mark the head of each jump table so that in the next pass, + * we know when a given jump table ends and the next one starts. + */ +static void mark_func_jump_tables(struct objtool_file *file, + struct symbol *func) { - struct instruction *insn, *last = NULL, *prev_jump = NULL; - struct rela *rela, *prev_rela = NULL; - int ret; + struct instruction *insn, *last = NULL; + struct rela *rela; func_for_each_insn_all(file, func, insn) { if (!last) @@ -1102,26 +1106,24 @@ static int add_func_jump_tables(struct objtool_file *file, continue; rela = find_jump_table(file, func, insn); - if (!rela) - continue; - - /* - * We found a jump table, but we don't know yet how big it - * is. Don't add it until we reach the end of the function or - * the beginning of another jump table in the same function. - */ - if (prev_jump) { - ret = add_jump_table(file, prev_jump, prev_rela, rela); - if (ret) - return ret; + if (rela) { + rela->jump_table_start = true; + insn->jump_table = rela; } - - prev_jump = insn; - prev_rela = rela; } +} + +static int add_func_jump_tables(struct objtool_file *file, + struct symbol *func) +{ + struct instruction *insn; + int ret; + + func_for_each_insn_all(file, func, insn) { + if (!insn->jump_table) + continue; - if (prev_jump) { - ret = add_jump_table(file, prev_jump, prev_rela, NULL); + ret = add_jump_table(file, insn, insn->jump_table); if (ret) return ret; } @@ -1148,6 +1150,7 @@ static int add_jump_table_alts(struct objtool_file *file) if (func->type != STT_FUNC) continue; + mark_func_jump_tables(file, func); ret = add_func_jump_tables(file, func); if (ret) return ret; diff --git a/tools/objtool/check.h b/tools/objtool/check.h index cb60b9acf5cf..afa6a79e0715 100644 --- a/tools/objtool/check.h +++ b/tools/objtool/check.h @@ -38,6 +38,7 @@ struct instruction { struct symbol *call_dest; struct instruction *jump_dest; struct instruction *first_jump_src; + struct rela *jump_table; struct list_head alts; struct symbol *func; struct stack_op stack_op; diff --git a/tools/objtool/elf.h b/tools/objtool/elf.h index d4d3e0528d4a..44150204db4d 100644 --- a/tools/objtool/elf.h +++ b/tools/objtool/elf.h @@ -62,6 +62,7 @@ struct rela { unsigned int type; unsigned long offset; int addend; + bool jump_table_start; }; struct elf { -- cgit v1.2.3