From: Guo Ren guoren@linux.alibaba.com
commit 6724a76cff85ee271bbbff42ac527e4643b2ec52 upstream.
Use a temporary register to reduce the size of detour code from 16 bytes to 8 bytes. The previous implementation is from 'commit afc76b8b8011 ("riscv: Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT")'.
Before the patch: <func_prolog>: 0: REG_S ra, -SZREG(sp) 4: auipc ra, ? 8: jalr ?(ra) 12: REG_L ra, -SZREG(sp) (func_boddy)
After the patch: <func_prolog>: 0: auipc t0, ? 4: jalr t0, ?(t0) (func_boddy)
This patch not just reduces the size of detour code, but also fixes an important issue:
An Ftrace callback registered with FTRACE_OPS_FL_IPMODIFY flag can actually change the instruction pointer, e.g. to "replace" the given kernel function with a new one, which is needed for livepatching, etc.
In this case, the trampoline (ftrace_regs_caller) would not return to <func_prolog+12> but would rather jump to the new function. So, "REG_L ra, -SZREG(sp)" would not run and the original return address would not be restored. The kernel is likely to hang or crash as a result.
This can be easily demonstrated if one tries to "replace", say, cmdline_proc_show() with a new function with the same signature using instruction_pointer_set(&fregs->regs, new_func_addr) in the Ftrace callback.
Link: https://lore.kernel.org/linux-riscv/20221122075440.1165172-1-suagrfillet@gma... Link: https://lore.kernel.org/linux-riscv/d7d5730b-ebef-68e5-5046-e763e1ee6164@yad... Co-developed-by: Song Shuai suagrfillet@gmail.com Signed-off-by: Song Shuai suagrfillet@gmail.com Signed-off-by: Guo Ren guoren@linux.alibaba.com Signed-off-by: Guo Ren guoren@kernel.org Cc: Evgenii Shatokhin e.shatokhin@yadro.com Reviewed-by: Evgenii Shatokhin e.shatokhin@yadro.com Link: https://lore.kernel.org/r/20230112090603.1295340-4-guoren@kernel.org Cc: stable@vger.kernel.org Fixes: 10626c32e382 ("riscv/ftrace: Add basic support") Signed-off-by: Palmer Dabbelt palmer@rivosinc.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/riscv/Makefile | 4 +- arch/riscv/include/asm/ftrace.h | 50 +++++++++++++++++++++++------- arch/riscv/kernel/ftrace.c | 65 +++++++++++----------------------------- arch/riscv/kernel/mcount-dyn.S | 42 +++++++++---------------- 4 files changed, 75 insertions(+), 86 deletions(-)
--- a/arch/riscv/Makefile +++ b/arch/riscv/Makefile @@ -12,9 +12,9 @@ ifeq ($(CONFIG_DYNAMIC_FTRACE),y) LDFLAGS_vmlinux := --no-relax KBUILD_CPPFLAGS += -DCC_USING_PATCHABLE_FUNCTION_ENTRY ifeq ($(CONFIG_RISCV_ISA_C),y) - CC_FLAGS_FTRACE := -fpatchable-function-entry=8 -else CC_FLAGS_FTRACE := -fpatchable-function-entry=4 +else + CC_FLAGS_FTRACE := -fpatchable-function-entry=2 endif endif
--- a/arch/riscv/include/asm/ftrace.h +++ b/arch/riscv/include/asm/ftrace.h @@ -42,6 +42,14 @@ struct dyn_arch_ftrace { * 2) jalr: setting low-12 offset to ra, jump to ra, and set ra to * return address (original pc + 4) * + *<ftrace enable>: + * 0: auipc t0/ra, 0x? + * 4: jalr t0/ra, ?(t0/ra) + * + *<ftrace disable>: + * 0: nop + * 4: nop + * * Dynamic ftrace generates probes to call sites, so we must deal with * both auipc and jalr at the same time. */ @@ -52,25 +60,43 @@ struct dyn_arch_ftrace { #define AUIPC_OFFSET_MASK (0xfffff000) #define AUIPC_PAD (0x00001000) #define JALR_SHIFT 20 -#define JALR_BASIC (0x000080e7) -#define AUIPC_BASIC (0x00000097) +#define JALR_RA (0x000080e7) +#define AUIPC_RA (0x00000097) +#define JALR_T0 (0x000282e7) +#define AUIPC_T0 (0x00000297) #define NOP4 (0x00000013)
-#define make_call(caller, callee, call) \ +#define to_jalr_t0(offset) \ + (((offset & JALR_OFFSET_MASK) << JALR_SHIFT) | JALR_T0) + +#define to_auipc_t0(offset) \ + ((offset & JALR_SIGN_MASK) ? \ + (((offset & AUIPC_OFFSET_MASK) + AUIPC_PAD) | AUIPC_T0) : \ + ((offset & AUIPC_OFFSET_MASK) | AUIPC_T0)) + +#define make_call_t0(caller, callee, call) \ do { \ - call[0] = to_auipc_insn((unsigned int)((unsigned long)callee - \ - (unsigned long)caller)); \ - call[1] = to_jalr_insn((unsigned int)((unsigned long)callee - \ - (unsigned long)caller)); \ + unsigned int offset = \ + (unsigned long) callee - (unsigned long) caller; \ + call[0] = to_auipc_t0(offset); \ + call[1] = to_jalr_t0(offset); \ } while (0)
-#define to_jalr_insn(offset) \ - (((offset & JALR_OFFSET_MASK) << JALR_SHIFT) | JALR_BASIC) +#define to_jalr_ra(offset) \ + (((offset & JALR_OFFSET_MASK) << JALR_SHIFT) | JALR_RA)
-#define to_auipc_insn(offset) \ +#define to_auipc_ra(offset) \ ((offset & JALR_SIGN_MASK) ? \ - (((offset & AUIPC_OFFSET_MASK) + AUIPC_PAD) | AUIPC_BASIC) : \ - ((offset & AUIPC_OFFSET_MASK) | AUIPC_BASIC)) + (((offset & AUIPC_OFFSET_MASK) + AUIPC_PAD) | AUIPC_RA) : \ + ((offset & AUIPC_OFFSET_MASK) | AUIPC_RA)) + +#define make_call_ra(caller, callee, call) \ +do { \ + unsigned int offset = \ + (unsigned long) callee - (unsigned long) caller; \ + call[0] = to_auipc_ra(offset); \ + call[1] = to_jalr_ra(offset); \ +} while (0)
/* * Let auipc+jalr be the basic *mcount unit*, so we make it 8 bytes here. --- a/arch/riscv/kernel/ftrace.c +++ b/arch/riscv/kernel/ftrace.c @@ -55,12 +55,15 @@ static int ftrace_check_current_call(uns }
static int __ftrace_modify_call(unsigned long hook_pos, unsigned long target, - bool enable) + bool enable, bool ra) { unsigned int call[2]; unsigned int nops[2] = {NOP4, NOP4};
- make_call(hook_pos, target, call); + if (ra) + make_call_ra(hook_pos, target, call); + else + make_call_t0(hook_pos, target, call);
/* Replace the auipc-jalr pair at once. Return -EPERM on write error. */ if (patch_text_nosync @@ -70,42 +73,13 @@ static int __ftrace_modify_call(unsigned return 0; }
-/* - * Put 5 instructions with 16 bytes at the front of function within - * patchable function entry nops' area. - * - * 0: REG_S ra, -SZREG(sp) - * 1: auipc ra, 0x? - * 2: jalr -?(ra) - * 3: REG_L ra, -SZREG(sp) - * - * So the opcodes is: - * 0: 0xfe113c23 (sd)/0xfe112e23 (sw) - * 1: 0x???????? -> auipc - * 2: 0x???????? -> jalr - * 3: 0xff813083 (ld)/0xffc12083 (lw) - */ -#if __riscv_xlen == 64 -#define INSN0 0xfe113c23 -#define INSN3 0xff813083 -#elif __riscv_xlen == 32 -#define INSN0 0xfe112e23 -#define INSN3 0xffc12083 -#endif - -#define FUNC_ENTRY_SIZE 16 -#define FUNC_ENTRY_JMP 4 - int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr) { - unsigned int call[4] = {INSN0, 0, 0, INSN3}; - unsigned long target = addr; - unsigned long caller = rec->ip + FUNC_ENTRY_JMP; + unsigned int call[2];
- call[1] = to_auipc_insn((unsigned int)(target - caller)); - call[2] = to_jalr_insn((unsigned int)(target - caller)); + make_call_t0(rec->ip, addr, call);
- if (patch_text_nosync((void *)rec->ip, call, FUNC_ENTRY_SIZE)) + if (patch_text_nosync((void *)rec->ip, call, MCOUNT_INSN_SIZE)) return -EPERM;
return 0; @@ -114,15 +88,14 @@ int ftrace_make_call(struct dyn_ftrace * int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, unsigned long addr) { - unsigned int nops[4] = {NOP4, NOP4, NOP4, NOP4}; + unsigned int nops[2] = {NOP4, NOP4};
- if (patch_text_nosync((void *)rec->ip, nops, FUNC_ENTRY_SIZE)) + if (patch_text_nosync((void *)rec->ip, nops, MCOUNT_INSN_SIZE)) return -EPERM;
return 0; }
- /* * This is called early on, and isn't wrapped by * ftrace_arch_code_modify_{prepare,post_process}() and therefor doesn't hold @@ -144,10 +117,10 @@ int ftrace_init_nop(struct module *mod, int ftrace_update_ftrace_func(ftrace_func_t func) { int ret = __ftrace_modify_call((unsigned long)&ftrace_call, - (unsigned long)func, true); + (unsigned long)func, true, true); if (!ret) { ret = __ftrace_modify_call((unsigned long)&ftrace_regs_call, - (unsigned long)func, true); + (unsigned long)func, true, true); }
return ret; @@ -159,16 +132,16 @@ int ftrace_modify_call(struct dyn_ftrace unsigned long addr) { unsigned int call[2]; - unsigned long caller = rec->ip + FUNC_ENTRY_JMP; + unsigned long caller = rec->ip; int ret;
- make_call(caller, old_addr, call); + make_call_t0(caller, old_addr, call); ret = ftrace_check_current_call(caller, call);
if (ret) return ret;
- return __ftrace_modify_call(caller, addr, true); + return __ftrace_modify_call(caller, addr, true, false); } #endif
@@ -203,12 +176,12 @@ int ftrace_enable_ftrace_graph_caller(vo int ret;
ret = __ftrace_modify_call((unsigned long)&ftrace_graph_call, - (unsigned long)&prepare_ftrace_return, true); + (unsigned long)&prepare_ftrace_return, true, true); if (ret) return ret;
return __ftrace_modify_call((unsigned long)&ftrace_graph_regs_call, - (unsigned long)&prepare_ftrace_return, true); + (unsigned long)&prepare_ftrace_return, true, true); }
int ftrace_disable_ftrace_graph_caller(void) @@ -216,12 +189,12 @@ int ftrace_disable_ftrace_graph_caller(v int ret;
ret = __ftrace_modify_call((unsigned long)&ftrace_graph_call, - (unsigned long)&prepare_ftrace_return, false); + (unsigned long)&prepare_ftrace_return, false, true); if (ret) return ret;
return __ftrace_modify_call((unsigned long)&ftrace_graph_regs_call, - (unsigned long)&prepare_ftrace_return, false); + (unsigned long)&prepare_ftrace_return, false, true); } #endif /* CONFIG_DYNAMIC_FTRACE */ #endif /* CONFIG_FUNCTION_GRAPH_TRACER */ --- a/arch/riscv/kernel/mcount-dyn.S +++ b/arch/riscv/kernel/mcount-dyn.S @@ -13,8 +13,8 @@
.text
-#define FENTRY_RA_OFFSET 12 -#define ABI_SIZE_ON_STACK 72 +#define FENTRY_RA_OFFSET 8 +#define ABI_SIZE_ON_STACK 80 #define ABI_A0 0 #define ABI_A1 8 #define ABI_A2 16 @@ -23,10 +23,10 @@ #define ABI_A5 40 #define ABI_A6 48 #define ABI_A7 56 -#define ABI_RA 64 +#define ABI_T0 64 +#define ABI_RA 72
.macro SAVE_ABI - addi sp, sp, -SZREG addi sp, sp, -ABI_SIZE_ON_STACK
REG_S a0, ABI_A0(sp) @@ -37,6 +37,7 @@ REG_S a5, ABI_A5(sp) REG_S a6, ABI_A6(sp) REG_S a7, ABI_A7(sp) + REG_S t0, ABI_T0(sp) REG_S ra, ABI_RA(sp) .endm
@@ -49,24 +50,18 @@ REG_L a5, ABI_A5(sp) REG_L a6, ABI_A6(sp) REG_L a7, ABI_A7(sp) + REG_L t0, ABI_T0(sp) REG_L ra, ABI_RA(sp)
addi sp, sp, ABI_SIZE_ON_STACK - addi sp, sp, SZREG .endm
#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS .macro SAVE_ALL - addi sp, sp, -SZREG addi sp, sp, -PT_SIZE_ON_STACK
- REG_S x1, PT_EPC(sp) - addi sp, sp, PT_SIZE_ON_STACK - REG_L x1, (sp) - addi sp, sp, -PT_SIZE_ON_STACK + REG_S t0, PT_EPC(sp) REG_S x1, PT_RA(sp) - REG_L x1, PT_EPC(sp) - REG_S x2, PT_SP(sp) REG_S x3, PT_GP(sp) REG_S x4, PT_TP(sp) @@ -100,15 +95,11 @@ .endm
.macro RESTORE_ALL + REG_L t0, PT_EPC(sp) REG_L x1, PT_RA(sp) - addi sp, sp, PT_SIZE_ON_STACK - REG_S x1, (sp) - addi sp, sp, -PT_SIZE_ON_STACK - REG_L x1, PT_EPC(sp) REG_L x2, PT_SP(sp) REG_L x3, PT_GP(sp) REG_L x4, PT_TP(sp) - REG_L x5, PT_T0(sp) REG_L x6, PT_T1(sp) REG_L x7, PT_T2(sp) REG_L x8, PT_S0(sp) @@ -137,17 +128,16 @@ REG_L x31, PT_T6(sp)
addi sp, sp, PT_SIZE_ON_STACK - addi sp, sp, SZREG .endm #endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
ENTRY(ftrace_caller) SAVE_ABI
- addi a0, ra, -FENTRY_RA_OFFSET + addi a0, t0, -FENTRY_RA_OFFSET la a1, function_trace_op REG_L a2, 0(a1) - REG_L a1, ABI_SIZE_ON_STACK(sp) + mv a1, ra mv a3, sp
ftrace_call: @@ -155,8 +145,8 @@ ftrace_call: call ftrace_stub
#ifdef CONFIG_FUNCTION_GRAPH_TRACER - addi a0, sp, ABI_SIZE_ON_STACK - REG_L a1, ABI_RA(sp) + addi a0, sp, ABI_RA + REG_L a1, ABI_T0(sp) addi a1, a1, -FENTRY_RA_OFFSET #ifdef HAVE_FUNCTION_GRAPH_FP_TEST mv a2, s0 @@ -166,17 +156,17 @@ ftrace_graph_call: call ftrace_stub #endif RESTORE_ABI - ret + jr t0 ENDPROC(ftrace_caller)
#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS ENTRY(ftrace_regs_caller) SAVE_ALL
- addi a0, ra, -FENTRY_RA_OFFSET + addi a0, t0, -FENTRY_RA_OFFSET la a1, function_trace_op REG_L a2, 0(a1) - REG_L a1, PT_SIZE_ON_STACK(sp) + mv a1, ra mv a3, sp
ftrace_regs_call: @@ -196,6 +186,6 @@ ftrace_graph_regs_call: #endif
RESTORE_ALL - ret + jr t0 ENDPROC(ftrace_regs_caller) #endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */