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Commit d05c5130 authored by Marcin Nowakowski's avatar Marcin Nowakowski Committed by Ralf Baechle
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MIPS: tracing: disable uprobe/kprobe on compact branch instructions 



Current instruction decoder for uprobe/kprobe handler only handles
branches with delay slots. For compact branches the behaviour is rather
unpredictable - and depending on the encoding of a compact branch
instruction may result in one (or more) of:
- executing an instruction that follows a branch which wasn't in a delay
  slot and shouldn't have been executed
- incorrectly emulating a branch leading to a jump to a wrong location
- unexpected branching out of the single-stepped code and never reaching
  the breakpoint that should terminate the probe handler

Results of these actions are generally unpredictable, but can end up
with a probed application or kernel crash, so disable placing probes on
compact branches until they are handled properly.

Signed-off-by: default avatarMarcin Nowakowski <marcin.nowakowski@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/14336/


Signed-off-by: default avatarRalf Baechle <ralf@linux-mips.org>
parent e3031b32

arch/mips/kernel/branch.c

+34 −0
Original line number Diff line number Diff line
@@ -866,3 +866,37 @@ int __compute_return_epc(struct pt_regs *regs) 
	force_sig(SIGBUS, current);

	return -EFAULT;

}



#if (defined CONFIG_KPROBES) || (defined CONFIG_UPROBES)



int __insn_is_compact_branch(union mips_instruction insn)

{

	if (!cpu_has_mips_r6)

		return 0;



	switch (insn.i_format.opcode) {

	case blezl_op:

	case bgtzl_op:

	case blez_op:

	case bgtz_op:

		/*

		 * blez[l] and bgtz[l] opcodes with non-zero rt

		 * are MIPS R6 compact branches

		 */

		if (insn.i_format.rt)

			return 1;

		break;

	case bc6_op:

	case balc6_op:

	case pop10_op:

	case pop30_op:

	case pop66_op:

	case pop76_op:

		return 1;

	}



	return 0;

}

EXPORT_SYMBOL_GPL(__insn_is_compact_branch);



#endif  /* CONFIG_KPROBES || CONFIG_UPROBES */

arch/mips/kernel/kprobes.c

+6 −0
Original line number Diff line number Diff line
@@ -106,6 +106,12 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p) 
		goto out;

	}



	if (__insn_is_compact_branch(insn)) {

		pr_notice("Kprobes for compact branches are not supported\n");

		ret = -EINVAL;

		goto out;

	}



	/* insn: must be on special executable page on mips. */

	p->ainsn.insn = get_insn_slot();

	if (!p->ainsn.insn) {

arch/mips/kernel/probes-common.h

+2 −0
Original line number Diff line number Diff line
@@ -13,6 +13,8 @@ 


#include <asm/inst.h>



int __insn_is_compact_branch(union mips_instruction insn);



static inline int __insn_has_delay_slot(const union mips_instruction insn)

{

	switch (insn.i_format.opcode) {

arch/mips/kernel/uprobes.c

+6 −0
Original line number Diff line number Diff line
@@ -36,6 +36,12 @@ int arch_uprobe_analyze_insn(struct arch_uprobe *aup, 
		return -EINVAL;



	inst.word = aup->insn[0];



	if (__insn_is_compact_branch(inst)) {

		pr_notice("Uprobes for compact branches are not supported\n");

		return -EINVAL;

	}



	aup->ixol[0] = aup->insn[insn_has_delay_slot(inst)];

	aup->ixol[1] = UPROBE_BRK_UPROBE_XOL;		/* NOP  */