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Message-Id: <20190605131945.005681046@infradead.org>
Date: Wed, 05 Jun 2019 15:08:01 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: x86@...nel.org
Cc: linux-kernel@...r.kernel.org,
Ard Biesheuvel <ard.biesheuvel@...aro.org>,
Andy Lutomirski <luto@...nel.org>,
Steven Rostedt <rostedt@...dmis.org>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Masami Hiramatsu <mhiramat@...nel.org>,
Jason Baron <jbaron@...mai.com>, Jiri Kosina <jkosina@...e.cz>,
David Laight <David.Laight@...LAB.COM>,
Borislav Petkov <bp@...en8.de>,
Julia Cartwright <julia@...com>, Jessica Yu <jeyu@...nel.org>,
"H. Peter Anvin" <hpa@...or.com>, Nadav Amit <namit@...are.com>,
Rasmus Villemoes <linux@...musvillemoes.dk>,
Edward Cree <ecree@...arflare.com>,
Daniel Bristot de Oliveira <bristot@...hat.com>
Subject: [PATCH 08/15] x86/alternatives: Teach text_poke_bp() to emulate instructions
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.
Cc: Daniel Bristot de Oliveira <bristot@...hat.com>
Cc: Nadav Amit <namit@...are.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
arch/x86/include/asm/text-patching.h | 2 -
arch/x86/kernel/alternative.c | 47 ++++++++++++++++++++++++++---------
arch/x86/kernel/jump_label.c | 3 --
arch/x86/kernel/kprobes/opt.c | 11 +++++---
4 files changed, 46 insertions(+), 17 deletions(-)
--- a/arch/x86/include/asm/text-patching.h
+++ b/arch/x86/include/asm/text-patching.h
@@ -37,7 +37,7 @@ 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 int after_bootmem;
extern __ro_after_init struct mm_struct *poking_mm;
extern __ro_after_init unsigned long poking_addr;
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -921,19 +921,25 @@ static void do_sync_core(void *info)
}
static bool bp_patching_in_progress;
-static void *bp_int3_handler, *bp_int3_addr;
+static const void *bp_int3_opcode, *bp_int3_addr;
int poke_int3_handler(struct pt_regs *regs)
{
+ long ip = regs->ip - INT3_INSN_SIZE + CALL_INSN_SIZE;
+ struct opcode {
+ u8 insn;
+ s32 rel;
+ } __packed opcode;
+
/*
* Having observed our INT3 instruction, we now must observe
* bp_patching_in_progress.
*
- * in_progress = TRUE INT3
- * WMB RMB
- * write INT3 if (in_progress)
+ * in_progress = TRUE INT3
+ * WMB RMB
+ * write INT3 if (in_progress)
*
- * Idem for bp_int3_handler.
+ * Idem for bp_int3_opcode.
*/
smp_rmb();
@@ -943,8 +949,21 @@ int poke_int3_handler(struct pt_regs *re
if (user_mode(regs) || regs->ip != (unsigned long)bp_int3_addr)
return 0;
- /* set up the specified breakpoint handler */
- regs->ip = (unsigned long) bp_int3_handler;
+ opcode = *(struct opcode *)bp_int3_opcode;
+
+ switch (opcode.insn) {
+ case 0xE8: /* CALL */
+ int3_emulate_call(regs, ip + opcode.rel);
+ break;
+
+ case 0xE9: /* JMP */
+ int3_emulate_jmp(regs, ip + opcode.rel);
+ break;
+
+ default: /* assume NOP */
+ int3_emulate_jmp(regs, ip);
+ break;
+ }
return 1;
}
@@ -955,7 +974,7 @@ NOKPROBE_SYMBOL(poke_int3_handler);
* @addr: address to patch
* @opcode: opcode of new instruction
* @len: length to copy
- * @handler: address to jump to when the temporary breakpoint is hit
+ * @emulate: opcode to emulate, when NULL use @opcode
*
* Modify multi-byte instruction by using int3 breakpoint on SMP.
* We completely avoid stop_machine() here, and achieve the
@@ -970,19 +989,25 @@ NOKPROBE_SYMBOL(poke_int3_handler);
* replacing opcode
* - sync cores
*/
-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)
{
unsigned char int3 = 0xcc;
- bp_int3_handler = handler;
+ bp_int3_opcode = emulate ?: opcode;
bp_int3_addr = (u8 *)addr + sizeof(int3);
bp_patching_in_progress = true;
lockdep_assert_held(&text_mutex);
/*
+ * poke_int3_handler() relies on @opcode being a 5 byte instruction;
+ * notably a JMP, CALL or NOP5_ATOMIC.
+ */
+ BUG_ON(len != 5);
+
+ /*
* Corresponding read barrier in int3 notifier for making sure the
- * in_progress and handler are correctly ordered wrt. patching.
+ * in_progress and opcode are correctly ordered wrt. patching.
*/
smp_wmb();
--- a/arch/x86/kernel/jump_label.c
+++ b/arch/x86/kernel/jump_label.c
@@ -87,8 +87,7 @@ 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,
--- 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);
}
/*
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