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Subject[RFC PATCH v2 0/6] uprobes/x86: fix the reprel jmp/call handling
On 04/06, Oleg Nesterov wrote:
>
> OK. Please see the RFC changes. Obviously not for inclusion yet. And
> totally untested, except I verified that the test-case from 4/6 works.

Still not really tested, but seems to work.

Please see v2. All changes are minor except the s/ENOSYS/-ENOSYS/ fix.
Please see the intediff below. I also move "Introduce sizeof_long() ..."
to the head of this series.

Jim, I am still thinking how I can improve the commenents in 4/6 as you
asked me, and I obviously need to write the changelogs and change "ttt"
prefix.

Will you agree with s/ttt/branch/ ?

Do you think the code is fine in v2 ?

Oleg.


--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -500,16 +500,13 @@ static bool check_jmp_cond(struct arch_uprobe *auprobe, struct pt_regs *regs)
unsigned long flags = regs->flags;

switch (auprobe->ttt.opc1) {
- case 0x00: /* not a conditional jmp */
- return true;
-
#define DO(expr) \
return expr;
CASE_COND
#undef DO

- default:
- BUG();
+ default: /* not a conditional jmp */
+ return true;
}
}

@@ -520,7 +517,7 @@ static bool check_jmp_cond(struct arch_uprobe *auprobe, struct pt_regs *regs)
static bool ttt_emulate_op(struct arch_uprobe *auprobe, struct pt_regs *regs)
{
unsigned long new_ip = regs->ip += auprobe->ttt.ilen;
- unsigned long disp = auprobe->ttt.disp;
+ unsigned long disp = (long)auprobe->ttt.disp;

if (ttt_is_call(auprobe)) {
unsigned long new_sp = regs->sp - sizeof_long();
@@ -562,8 +559,8 @@ static void ttt_clear_displacement(struct arch_uprobe *auprobe, struct insn *ins
* divorce ->insn[] and ->ixol[]. We need to preserve the 1st byte
* of ->insn[] for set_orig_insn().
*/
- memset(auprobe->insn + insn_offset_displacement(insn),
- 0, insn->moffset1.nbytes);
+ memset(auprobe->insn + insn_offset_immediate(insn),
+ 0, insn->immediate.nbytes);
}

static struct uprobe_xol_ops ttt_xol_ops = {
@@ -571,6 +568,7 @@ static struct uprobe_xol_ops ttt_xol_ops = {
.post_xol = ttt_post_xol_op,
};

+/* Returns -ENOSYS if ttt_xol_ops doesn't handle this insn */
static int ttt_setup_xol_ops(struct arch_uprobe *auprobe, struct insn *insn)
{
u8 opc1 = OPCODE1(insn);
@@ -588,24 +586,24 @@ static int ttt_setup_xol_ops(struct arch_uprobe *auprobe, struct insn *insn)

case 0xe8: /* call relative */
ttt_clear_displacement(auprobe, insn);
- auprobe->ttt.opc1 = opc1;
break;

case 0x0f:
if (insn->opcode.nbytes != 2)
return -ENOSYS;
+ /*
+ * If it is a "near" conditional jmp, OPCODE2() - 0x10 matches
+ * OPCODE1() of the "short" jmp which checks the same condition.
+ */
opc1 = OPCODE2(insn) - 0x10;
default:
if (!is_cond_jmp_opcode(opc1))
return -ENOSYS;
- auprobe->ttt.opc1 = opc1;
}

+ auprobe->ttt.opc1 = opc1;
auprobe->ttt.ilen = insn->length;
- auprobe->ttt.disp = insn->moffset1.value;
- /* so far we assume that it fits into ->moffset1 */
- if (WARN_ON_ONCE(insn->moffset2.nbytes))
- return -ENOEXEC;
+ auprobe->ttt.disp = insn->immediate.value;

auprobe->ops = &ttt_xol_ops;
return 0;
@@ -629,7 +627,7 @@ int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe, struct mm_struct *mm,
return ret;

ret = ttt_setup_xol_ops(auprobe, &insn);
- if (ret == 0 || ret != ENOSYS)
+ if (ret != -ENOSYS)
return ret;

/*


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