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Subject[RFC][PROTO][PATCH -tip 7/7] kprobes: x86: check specified probe can be optimized
Introduce can_optimize() function for ensuring that user specified probe
address can be jump optimized by decoding instructions.
This function decodes whole of a function in which probe is inserted, and
checks following condition:
- There is no indirect jump instruction, because it will jumps into
the address range which is replaced by jump oprand.
- There is no jump/loop instruction which jumps into the address range
which is replaced by jump oprand.

Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
---
arch/x86/kernel/kprobes.c | 75 +++++++++++++++++++++++++++++++++++++++++++++
1 files changed, 75 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/kprobes.c b/arch/x86/kernel/kprobes.c
index 5635e02..1386e34 100644
--- a/arch/x86/kernel/kprobes.c
+++ b/arch/x86/kernel/kprobes.c
@@ -1253,6 +1253,78 @@ static int __kprobes prepare_copied_insn(u8 *buf, struct optimized_kprobe *op)
return len;
}

+/* Dummy buffers for lookup_symbol_attrs */
+static char __dummy_buf[KSYM_NAME_LEN];
+
+/* Check whether insn is indirect jump */
+static int insn_is_indirect_jump(struct insn *insn)
+{
+ return (OPCODE1(insn) == 0xff || OPCODE1(insn) == 0xea);
+}
+
+/* Check whether insn jumps into specified address range */
+static int insn_jump_into_range(struct insn *insn, unsigned long start, int len)
+{
+ unsigned long target = 0;
+ switch (OPCODE1(insn)) {
+ case 0xe0: /* loopne */
+ case 0xe1: /* loope */
+ case 0xe2: /* loop */
+ case 0xe3: /* jcxz */
+ case 0xe9: /* near relative jump */
+ case 0xeb: /* short relative jump */
+ break;
+ case 0x0f:
+ if ((OPCODE2(insn) & 0xf0) == 0x80) /* jcc near */
+ break;
+ return 0;
+ default:
+ if ((OPCODE1(insn) & 0xf0) == 0x70) /* jcc short */
+ break;
+ return 0;
+ }
+ target = (unsigned long)insn->next_byte + insn->immediate.value;
+ return (start <= target && target <= start + len);
+}
+
+/* Decode whole function to ensure any instructions don't jump into target */
+static int __kprobes can_optimize(unsigned long paddr)
+{
+ int ret;
+ unsigned long addr, size = 0, offset = 0;
+ struct insn insn;
+ kprobe_opcode_t buf[MAX_INSN_SIZE];
+
+ /* Lookup symbol including addr */
+ if (!kallsyms_lookup(paddr, &size, &offset, NULL, __dummy_buf))
+ return 0;
+
+ /* Decode instructions */
+ addr = paddr - offset;
+ while (addr < paddr - offset + size) { /* Decode until function end */
+ insn_init_kernel(&insn, (void *)addr);
+ insn_get_opcode(&insn);
+ if (OPCODE1(&insn) == BREAKPOINT_INSTRUCTION) {
+ ret = recover_probed_instruction(buf, addr);
+ if (ret)
+ return 0;
+ insn_init_kernel(&insn, buf);
+ }
+ insn_get_length(&insn);
+ /* Recover address */
+ insn.kaddr = (void *)addr;
+ insn.next_byte = (void *)(addr + insn.length);
+ /* Check any instructions don't jump into target */
+ if (insn_is_indirect_jump(&insn) ||
+ insn_jump_into_range(&insn, addr + INT3_SIZE,
+ RELATIVE_ADDR_SIZE))
+ return 0;
+ addr += insn.length;
+ }
+
+ return 1;
+}
+
int arch_optimized_kprobe_address(struct optimized_kprobe *op,
unsigned long addr)
{
@@ -1269,6 +1341,9 @@ int __kprobes arch_prepare_optimized_kprobe(struct optimized_kprobe *op)
u8 *buf;
int ret, i;

+ if (!can_optimize((unsigned long)op->kp.addr))
+ return -EINVAL;
+
op->optinsn.insn = get_optinsn_slot();
if (!op->optinsn.insn)
return -ENOMEM;
--
Masami Hiramatsu
Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division

e-mail: mhiramat@redhat.com



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