Re: [PATCH V6 0/6] x86/jump_label: Bound IPIs sent when updating a static key

Daniel Bristot de Oliveira
2019-06-13T16:33:35Z

On 12/06/2019 19:07, Peter Zijlstra wrote:
> On Wed, Jun 12, 2019 at 11:57:25AM +0200, Daniel Bristot de Oliveira wrote:
>> Daniel Bristot de Oliveira (6):
>> jump_label: Add a jump_label_can_update() helper
>> x86/jump_label: Add a __jump_label_set_jump_code() helper
>> jump_label: Sort entries of the same key by the code
>> x86/alternative: Batch of patch operations
>> jump_label: Batch updates if arch supports it
>> x86/jump_label: Batch jump label updates
>>
>> arch/x86/include/asm/jump_label.h | 2 +
>> arch/x86/include/asm/text-patching.h | 15 +++
>> arch/x86/kernel/alternative.c | 154 +++++++++++++++++++++------
>> arch/x86/kernel/jump_label.c | 110 ++++++++++++++++---
>> include/linux/jump_label.h | 3 +
>> kernel/jump_label.c | 65 +++++++++--
>> 6 files changed, 290 insertions(+), 59 deletions(-)
>
> OK, so I like these. I did make me some change, but mostly cosmetic
> (although patch #2 got a bigger shuffle than intended).
>
> I've also done my text_poke_bp() emulation thing on top of this, to make
> sure it all works properly. Funnily, that shrank the size of
> text_poke_loc to 24 bytes and thus we now fit 170 locations in the one
> page.
>
> ---
> Subject: x86/alternatives: Teach text_poke_bp() to emulate instructions
> From: Peter Zijlstra <peterz@infradead.org>
> Date: Wed Jun 5 10:48:37 CEST 2019
>
> In preparation for static_call support, teach text_poke_bp() to
> emulate instructions, including CALL.
>
> The current text_poke_bp() takes a @handler argument which is used as
> a jump target when the temporary INT3 is hit by a different CPU.
>
> When patching CALL instructions, this doesn't work because we'd miss
> the PUSH of the return address. Instead, teach poke_int3_handler() to
> emulate an instruction, typically the instruction we're patching in.
>
> This fits almost all text_poke_bp() users, except
> arch_unoptimize_kprobe() which restores random text, and for that site
> we have to build an explicit emulate instruction.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
> arch/x86/include/asm/text-patching.h | 24 +++++++--
> arch/x86/kernel/alternative.c | 88 +++++++++++++++++++++++++----------
> arch/x86/kernel/jump_label.c | 9 +--
> arch/x86/kernel/kprobes/opt.c | 11 +++-
> 4 files changed, 93 insertions(+), 39 deletions(-)
>
> --- a/arch/x86/include/asm/text-patching.h
> +++ b/arch/x86/include/asm/text-patching.h
> @@ -26,10 +26,11 @@ static inline void apply_paravirt(struct
> #define POKE_MAX_OPCODE_SIZE 5
>
> struct text_poke_loc {
> - void *detour;
> void *addr;
> - size_t len;
> - const char opcode[POKE_MAX_OPCODE_SIZE];
> + int len;
> + s32 rel32;
> + u8 opcode;
> + const char text[POKE_MAX_OPCODE_SIZE];
> };
>
> extern void text_poke_early(void *addr, const void *opcode, size_t len);
> @@ -51,8 +52,10 @@ extern void text_poke_early(void *addr,
> extern void *text_poke(void *addr, const void *opcode, size_t len);
> extern void *text_poke_kgdb(void *addr, const void *opcode, size_t len);
> extern int poke_int3_handler(struct pt_regs *regs);
> -extern void text_poke_bp(void *addr, const void *opcode, size_t len, void *handler);
> +extern void text_poke_bp(void *addr, const void *opcode, size_t len, const void *emulate);
> extern void text_poke_bp_batch(struct text_poke_loc *tp, unsigned int nr_entries);
> +extern void text_poke_loc_init(struct text_poke_loc *tp, void *addr,
> + const void *opcode, size_t len, const void *emulate);
> extern int after_bootmem;
> extern __ro_after_init struct mm_struct *poking_mm;
> extern __ro_after_init unsigned long poking_addr;
> @@ -63,8 +66,17 @@ static inline void int3_emulate_jmp(stru
> regs->ip = ip;
> }
>
> -#define INT3_INSN_SIZE 1
> -#define CALL_INSN_SIZE 5
> +#define INT3_INSN_SIZE 1
> +#define INT3_INSN_OPCODE 0xCC
> +
> +#define CALL_INSN_SIZE 5
> +#define CALL_INSN_OPCODE 0xE9
> +
> +#define JMP32_INSN_SIZE 5
> +#define JMP32_INSN_OPCODE 0xE8
> +
> +#define JMP8_INSN_SIZE 2
> +#define JMP8_INSN_OPCODE 0xEB
>
> static inline void int3_emulate_push(struct pt_regs *regs, unsigned long val)
> {
> --- a/arch/x86/kernel/alternative.c
> +++ b/arch/x86/kernel/alternative.c
> @@ -941,16 +941,15 @@ NOKPROBE_SYMBOL(patch_cmp);
> int poke_int3_handler(struct pt_regs *regs)
> {
> struct text_poke_loc *tp;
> - unsigned char int3 = 0xcc;
> void *ip;
>
> /*
> * Having observed our INT3 instruction, we now must observe
> * bp_patching.nr_entries.
> *
> - * nr_entries != 0 INT3
> - * WMB RMB
> - * write INT3 if (nr_entries)
> + * nr_entries != 0 INT3
> + * WMB RMB
> + * write INT3 if (nr_entries)
> *
> * Idem for other elements in bp_patching.
> */
> @@ -963,9 +962,9 @@ int poke_int3_handler(struct pt_regs *re
> return 0;
>
> /*
> - * Discount the sizeof(int3). See text_poke_bp_batch().
> + * Discount the INT3. See text_poke_bp_batch().
> */
> - ip = (void *) regs->ip - sizeof(int3);
> + ip = (void *) regs->ip - INT3_INSN_SIZE;
>
> /*
> * Skip the binary search if there is a single member in the vector.
> @@ -982,8 +981,22 @@ int poke_int3_handler(struct pt_regs *re
> return 0;
> }
>
> - /* set up the specified breakpoint detour */
> - regs->ip = (unsigned long) tp->detour;
> + ip += tp->len;
> +
> + switch (tp->opcode) {
> + case CALL_INSN_OPCODE:
> + int3_emulate_call(regs, (long)ip + tp->rel32);
> + break;
> +
> + case JMP32_INSN_OPCODE:
> + case JMP8_INSN_OPCODE:
> + int3_emulate_jmp(regs, (long)ip + tp->rel32);
> + break;
> +
> + default: /* nop */
> + int3_emulate_jmp(regs, (long)ip);
> + break;
> + }
>
> return 1;
> }
> @@ -1012,8 +1025,8 @@ NOKPROBE_SYMBOL(poke_int3_handler);
> */
> void text_poke_bp_batch(struct text_poke_loc *tp, unsigned int nr_entries)
> {
> + unsigned char int3 = INT3_INSN_OPCODE;
> int patched_all_but_first = 0;
> - unsigned char int3 = 0xcc;
> unsigned int i;
>
> lockdep_assert_held(&text_mutex);
> @@ -1041,7 +1054,7 @@ void text_poke_bp_batch(struct text_poke
> for (i = 0; i < nr_entries; i++) {
> if (tp[i].len - sizeof(int3) > 0) {
> text_poke((char *)tp[i].addr + sizeof(int3),
> - (const char *)tp[i].opcode + sizeof(int3),
> + (const char *)tp[i].text + sizeof(int3),
> tp[i].len - sizeof(int3));
> patched_all_but_first++;
> }
> @@ -1061,7 +1074,7 @@ void text_poke_bp_batch(struct text_poke
> * replacing opcode.
> */
> for (i = 0; i < nr_entries; i++)
> - text_poke(tp[i].addr, tp[i].opcode, sizeof(int3));
> + text_poke(tp[i].addr, tp[i].text, sizeof(int3));
>
> on_each_cpu(do_sync_core, NULL, 1);
> /*
> @@ -1072,6 +1085,43 @@ void text_poke_bp_batch(struct text_poke
> bp_patching.nr_entries = 0;
> }
>
> +void text_poke_loc_init(struct text_poke_loc *tp, void *addr,
> + const void *opcode, size_t len, const void *emulate)
> +{
> + struct insn insn;
> +
> + if (!opcode)
> + opcode = (void *)tp->text;
> + else
> + memcpy((void *)tp->text, opcode, len);
> +
> + if (!emulate)
> + emulate = opcode;
> +
> + kernel_insn_init(&insn, emulate, MAX_INSN_SIZE);
> + insn_get_length(&insn);
> +
> + BUG_ON(!insn_complete(&insn));
> + BUG_ON(len != insn.length);
> +
> + tp->addr = addr;
> + tp->len = len;
> + tp->opcode = insn.opcode.bytes[0];
> +
> + switch (tp->opcode) {
> + case CALL_INSN_OPCODE:
> + case JMP32_INSN_OPCODE:
> + case JMP8_INSN_OPCODE:
> + tp->rel32 = insn.immediate.value;
> + break;
> +
> + default:
> + BUG_ON(len != 5);
> + BUG_ON(memcmp(emulate, ideal_nops[NOP_ATOMIC5], len));
> + break;
> + }
> +}
> +
> /**
> * text_poke_bp() -- update instructions on live kernel on SMP
> * @addr: address to patch
> @@ -1083,20 +1133,10 @@ void text_poke_bp_batch(struct text_poke
> * dynamically allocated memory. This function should be used when it is
> * not possible to allocate memory.
> */
> -void text_poke_bp(void *addr, const void *opcode, size_t len, void *handler)
> +void text_poke_bp(void *addr, const void *opcode, size_t len, const void *emulate)
> {
> - struct text_poke_loc tp = {
> - .detour = handler,
> - .addr = addr,
> - .len = len,
> - };
> -
> - if (len > POKE_MAX_OPCODE_SIZE) {
> - WARN_ONCE(1, "len is larger than %d\n", POKE_MAX_OPCODE_SIZE);
> - return;
> - }
> -
> - memcpy((void *)tp.opcode, opcode, len);
> + struct text_poke_loc tp;
>
> + text_poke_loc_init(&tp, addr, opcode, len, emulate);
> text_poke_bp_batch(&tp, 1);
> }
> --- a/arch/x86/kernel/jump_label.c
> +++ b/arch/x86/kernel/jump_label.c
> @@ -89,8 +89,7 @@ static void __ref __jump_label_transform
> return;
> }
>
> - text_poke_bp((void *)jump_entry_code(entry), &code, JUMP_LABEL_NOP_SIZE,
> - (void *)jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE);
> + text_poke_bp((void *)jump_entry_code(entry), &code, JUMP_LABEL_NOP_SIZE, NULL);
> }
>
> void arch_jump_label_transform(struct jump_entry *entry,
> @@ -147,11 +146,9 @@ bool arch_jump_label_transform_queue(str
> }
>
> __jump_label_set_jump_code(entry, type,
> - (union jump_code_union *) &tp->opcode, 0);
> + (union jump_code_union *)&tp->text, 0);
>
> - tp->addr = entry_code;
> - tp->detour = entry_code + JUMP_LABEL_NOP_SIZE;
> - tp->len = JUMP_LABEL_NOP_SIZE;
> + text_poke_loc_init(tp, entry_code, NULL, JUMP_LABEL_NOP_SIZE, NULL);
>
> tp_vec_nr++;
>
> --- a/arch/x86/kernel/kprobes/opt.c
> +++ b/arch/x86/kernel/kprobes/opt.c
> @@ -437,8 +437,7 @@ void arch_optimize_kprobes(struct list_h
> insn_buff[0] = RELATIVEJUMP_OPCODE;
> *(s32 *)(&insn_buff[1]) = rel;
>
> - text_poke_bp(op->kp.addr, insn_buff, RELATIVEJUMP_SIZE,
> - op->optinsn.insn);
> + text_poke_bp(op->kp.addr, insn_buff, RELATIVEJUMP_SIZE, NULL);
>
> list_del_init(&op->list);
> }
> @@ -448,12 +447,18 @@ void arch_optimize_kprobes(struct list_h
> void arch_unoptimize_kprobe(struct optimized_kprobe *op)
> {
> u8 insn_buff[RELATIVEJUMP_SIZE];
> + u8 emulate_buff[RELATIVEJUMP_SIZE];
>
> /* Set int3 to first byte for kprobes */
> insn_buff[0] = BREAKPOINT_INSTRUCTION;
> memcpy(insn_buff + 1, op->optinsn.copied_insn, RELATIVE_ADDR_SIZE);
> +
> + emulate_buff[0] = RELATIVEJUMP_OPCODE;
> + *(s32 *)(&emulate_buff[1]) = (s32)((long)op->optinsn.insn -
> + ((long)op->kp.addr + RELATIVEJUMP_SIZE));
> +
> text_poke_bp(op->kp.addr, insn_buff, RELATIVEJUMP_SIZE,
> - op->optinsn.insn);
> + emulate_buff);
> }
>
> /*
>

Reviewed-by: Daniel Bristot de Oliveira <bristot@redhat.com>

Thanks Peter!
-- Daniel