It is possible to replace rip-relative addressing mode
with addressing mode of the same length: [reg+disp32].
This eliminates the need to fix up immediate.
Only
Signed-off-by: Denys Vlasenko <dvlas...@redhat.com>
CC: Jim Keniston <jkeni...@us.ibm.com>
CC: Masami Hiramatsu <masami.hiramatsu...@hitachi.com>
CC: Oleg Nesterov <o...@redhat.com>
---
arch/x86/include/asm/uprobes.h | 2 +-
arch/x86/kernel/uprobes.c | 30 +++++++++++++-----------------
2 files changed, 14 insertions(+), 18 deletions(-)
diff --git a/arch/x86/include/asm/uprobes.h b/arch/x86/include/asm/uprobes.h
index 93bee7b..9197119 100644
--- a/arch/x86/include/asm/uprobes.h
+++ b/arch/x86/include/asm/uprobes.h
@@ -46,7 +46,7 @@ struct arch_uprobe {
union {
#ifdef CONFIG_X86_64
- unsigned long rip_rela_target_address;
+ int insn_length;
#endif
struct {
s32 offs;
diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index 7021dbe..b461dda 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -349,7 +349,7 @@ static int validate_insn_32bits(struct arch_uprobe
*auprobe, struct insn *insn)
* If arch_uprobe->insn doesn't use rip-relative addressing, return
* immediately. Otherwise, rewrite the instruction so that it accesses
* its memory operand indirectly through a scratch register. Set
- * arch_uprobe->fixups and arch_uprobe->rip_rela_target_address
+ * arch_uprobe->fixups and arch_uprobe->insn_length
* accordingly. (The contents of the scratch register will be saved
* before we single-step the modified instruction, and restored
* afterward.)
@@ -395,9 +395,12 @@ handle_riprel_insn(struct arch_uprobe *auprobe, struct
insn *insn)
insn_get_length(insn);
/*
- * Convert from rip-relative addressing to indirect addressing
+ * Convert from rip-relative addressing to register-relative addressing
* via a scratch register. Change the r/m field from 0x5 (%rip)
- * to 0x0 (%rax) or 0x1 (%rcx), and squeeze out the offset field.
+ * to 0x0 (%rax) or 0x1 (%rcx), change mode field
+ * from 00 to 10 (reg+disp32). Example:
+ * 89 05 disp32 mov %eax,disp32(%rip) becomes
+ * 89 81 disp32 mov %eax,disp32(%rcx)
*/
reg = MODRM_REG(insn);
if (reg == 0) {
@@ -409,23 +412,16 @@ handle_riprel_insn(struct arch_uprobe *auprobe, struct
insn *insn)
* #1) for the scratch register.
*/
auprobe->fixups = UPROBE_FIX_RIP_CX;
- /* Change modrm from 00 000 101 to 00 000 001. */
- *cursor = 0x1;
+ /* Change modrm from 00 000 101 to 10 000 001. */
+ *cursor = 0x81;
} else {
/* Use %rax (register #0) for the scratch register. */
auprobe->fixups = UPROBE_FIX_RIP_AX;
- /* Change modrm from 00 xxx 101 to 00 xxx 000 */
- *cursor = (reg << 3);
+ /* Change modrm from 00 xxx 101 to 10 xxx 000 */
+ *cursor = (reg << 3) | 0x80;
}
- /* Target address = address of next instruction + (signed) offset */
- auprobe->rip_rela_target_address = (long)insn->length +
insn->displacement.value;
-
- /* Displacement field is gone; slide immediate field (if any) over. */
- if (insn->immediate.nbytes) {
- cursor++;
- memmove(cursor, cursor + insn->displacement.nbytes,
insn->immediate.nbytes);
- }
+ auprobe->insn_length = insn->length;
}
/*
@@ -439,11 +435,11 @@ pre_xol_rip_insn(struct arch_uprobe *auprobe, struct
pt_regs *regs,
if (auprobe->fixups & UPROBE_FIX_RIP_AX) {
autask->saved_scratch_register = regs->ax;
regs->ax = current->utask->vaddr;
- regs->ax += auprobe->rip_rela_target_address;
+ regs->ax += auprobe->insn_length;
} else if (auprobe->fixups & UPROBE_FIX_RIP_CX) {
autask->saved_scratch_register = regs->cx;
regs->cx = current->utask->vaddr;
- regs->cx += auprobe->rip_rela_target_address;
+ regs->cx += auprobe->insn_length;
}
}
--
1.8.1.4
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