Messages in this thread Patch in this message |  | | From | Tiezhu Yang <> | | Subject | [PATCH v2 2/3] objtool: Handle secondary stack related instructions | | Date | Mon, 5 Aug 2024 11:26:59 +0800 |
| |
After commit a0f7085f6a63 ("LoongArch: Add RANDOMIZE_KSTACK_OFFSET support"), there is a new instruction "sub.d $sp, $sp, $t0" for the secondary stack in do_syscall(), then there exists a objtool warning "do_syscall+0x11c: return with modified stack frame" and there is no handle_syscall() which is the previous frame of do_syscall() in the call trace when executing the command "echo l > /proc/sysrq-trigger".
objdump shows something like this:
0000000000000000 <do_syscall>: 0: 02ff8063 addi.d $sp, $sp, -32 4: 29c04076 st.d $fp, $sp, 16 8: 29c02077 st.d $s0, $sp, 8 c: 29c06061 st.d $ra, $sp, 24 10: 02c08076 addi.d $fp, $sp, 32 ... 74: 0011b063 sub.d $sp, $sp, $t0 ... a8: 4c000181 jirl $ra, $t0, 0 ... dc: 02ff82c3 addi.d $sp, $fp, -32 e0: 28c06061 ld.d $ra, $sp, 24 e4: 28c04076 ld.d $fp, $sp, 16 e8: 28c02077 ld.d $s0, $sp, 8 ec: 02c08063 addi.d $sp, $sp, 32 f0: 4c000020 jirl $zero, $ra, 0
The instruction "sub.d $sp, $sp, $t0" changes the stack bottom and the new stack size is a random value, in order to find the return address of do_syscall() which is stored in the original stack frame after executing "jirl $ra, $t0, 0", it should use fp which points to the original stack top.
This is a rare case, add a member "secondary_stack" in the struct symbol as a label to avoid affecting the current normal case, then set it as true only if there exists the secondary stack instruction "sub.d $sp, $sp, $t0", at last check this label for the other special secondary stack instructions about fp to change the cfa base and cfa offset during the period of secondary stack in update_cfi_state().
Tested with the following two configs: (1) CONFIG_RANDOMIZE_KSTACK_OFFSET=y && CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT=n (2) CONFIG_RANDOMIZE_KSTACK_OFFSET=y && CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT=y
Cc: stable@vger.kernel.org # 6.9+ Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn> --- tools/objtool/arch/loongarch/decode.c | 8 +++++++- tools/objtool/check.c | 22 ++++++++++++++++++++++ tools/objtool/include/objtool/elf.h | 1 + 3 files changed, 30 insertions(+), 1 deletion(-)
diff --git a/tools/objtool/arch/loongarch/decode.c b/tools/objtool/arch/loongarch/decode.c index db4dd05cdb49..4085714ffd18 100644 --- a/tools/objtool/arch/loongarch/decode.c +++ b/tools/objtool/arch/loongarch/decode.c @@ -122,7 +122,7 @@ static bool decode_insn_reg2i12_fomat(union loongarch_instruction inst, switch (inst.reg2i12_format.opcode) { case addid_op: if ((inst.reg2i12_format.rd == CFI_SP) || (inst.reg2i12_format.rj == CFI_SP)) { - /* addi.d sp,sp,si12 or addi.d fp,sp,si12 */ + /* addi.d sp,sp,si12 or addi.d fp,sp,si12 or addi.d sp,fp,si12 */ insn->immediate = sign_extend64(inst.reg2i12_format.immediate, 11); ADD_OP(op) { op->src.type = OP_SRC_ADD; @@ -275,6 +275,8 @@ static bool decode_insn_reg2i16_fomat(union loongarch_instruction inst, static bool decode_insn_reg3_fomat(union loongarch_instruction inst, struct instruction *insn) { + struct symbol *func; + switch (inst.reg3_format.opcode) { case subd_op: if ((inst.reg3_format.rd == CFI_SP) && (inst.reg3_format.rj == CFI_SP)) { @@ -282,6 +284,10 @@ static bool decode_insn_reg3_fomat(union loongarch_instruction inst, * sub.d sp,sp,t0 * this is a rare case for the secondary stack. */ + func = find_func_containing(insn->sec, insn->offset); + if (!func) + return false; + func->secondary_stack = true; } break; default: diff --git a/tools/objtool/check.c b/tools/objtool/check.c index 01237d167223..c7b9942fee29 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -2993,6 +2993,28 @@ static int update_cfi_state(struct instruction *insn, break; } + if (op->dest.reg == CFI_BP && op->src.reg == CFI_SP) { + /* addi.d fp,sp,imm for the secondary stack on LoongArch */ + if (cfa->base == CFI_SP && cfa->offset == op->src.offset) { + if (insn->sym->secondary_stack) { + cfa->base = CFI_BP; + cfa->offset = 0; + } + } + break; + } + + if (op->dest.reg == CFI_SP && op->src.reg == CFI_BP) { + /* addi.d sp,fp,imm for the secondary stack on LoongArch */ + if (cfa->base == CFI_FP && cfa->offset == 0) { + if (insn->sym->secondary_stack) { + cfa->base = CFI_SP; + cfa->offset = -op->src.offset; + } + } + break; + } + if (op->dest.reg == CFI_SP && op->src.reg == CFI_BP) { /* lea disp(%rbp), %rsp */ diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h index 2b8a69de4db8..586916e0d441 100644 --- a/tools/objtool/include/objtool/elf.h +++ b/tools/objtool/include/objtool/elf.h @@ -68,6 +68,7 @@ struct symbol { u8 warned : 1; u8 embedded_insn : 1; u8 local_label : 1; + u8 secondary_stack : 1; struct list_head pv_target; struct reloc *relocs; }; -- 2.42.0
|  |