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uprobes/x86: Emulate relative conditional "short" jmp's 

Teach branch_emulate_op() to emulate the conditional "short" jmp's which
check regs->flags.

Note: this doesn't support jcxz/jcexz, loope/loopz, and loopne/loopnz.
They all are rel8 and thus they can't trigger the problem, but perhaps
we will add the support in future just for completeness.

Reported-by: Jonathan Lebon <jlebon@redhat.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Jim Keniston <jkenisto@us.ibm.com>
This commit is contained in:
Oleg Nesterov 2014-04-06 21:53:47 +02:00
parent 8e89c0be17
commit 8f95505bc1
1 changed files with 55 additions and 2 deletions
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57
arch/x86/kernel/uprobes.c
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@ -466,9 +466,58 @@ static bool branch_is_call(struct arch_uprobe *auprobe)
return auprobe->branch.opc1 == 0xe8;
}
#define CASE_COND \
COND(70, 71, XF(OF)) \
COND(72, 73, XF(CF)) \
COND(74, 75, XF(ZF)) \
COND(78, 79, XF(SF)) \
COND(7a, 7b, XF(PF)) \
COND(76, 77, XF(CF) || XF(ZF)) \
COND(7c, 7d, XF(SF) != XF(OF)) \
COND(7e, 7f, XF(ZF) || XF(SF) != XF(OF))
#define COND(op_y, op_n, expr) \
case 0x ## op_y: DO((expr) != 0) \
case 0x ## op_n: DO((expr) == 0)
#define XF(xf) (!!(flags & X86_EFLAGS_ ## xf))
static bool is_cond_jmp_opcode(u8 opcode)
{
switch (opcode) {
#define DO(expr) \
return true;
CASE_COND
#undef DO
default:
return false;
}
}
static bool check_jmp_cond(struct arch_uprobe *auprobe, struct pt_regs *regs)
{
unsigned long flags = regs->flags;
switch (auprobe->branch.opc1) {
#define DO(expr) \
return expr;
CASE_COND
#undef DO
default: /* not a conditional jmp */
return true;
}
}
#undef XF
#undef COND
#undef CASE_COND
static bool branch_emulate_op(struct arch_uprobe *auprobe, struct pt_regs *regs)
{
unsigned long new_ip = regs->ip += auprobe->branch.ilen;
unsigned long offs = (long)auprobe->branch.offs;
if (branch_is_call(auprobe)) {
unsigned long new_sp = regs->sp - sizeof_long();
@ -484,9 +533,11 @@ static bool branch_emulate_op(struct arch_uprobe *auprobe, struct pt_regs *regs)
if (copy_to_user((void __user *)new_sp, &new_ip, sizeof_long()))
return false;
regs->sp = new_sp;
} else if (!check_jmp_cond(auprobe, regs)) {
offs = 0;
}
regs->ip = new_ip + auprobe->branch.offs;
regs->ip = new_ip + offs;
return true;
}
@ -547,8 +598,10 @@ static int branch_setup_xol_ops(struct arch_uprobe *auprobe, struct insn *insn)
case 0xe8: /* call relative */
branch_clear_offset(auprobe, insn);
break;
default:
return -ENOSYS;
if (!is_cond_jmp_opcode(opc1))
return -ENOSYS;
}
auprobe->branch.opc1 = opc1;