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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: Marcin Nowakowski <marcin.nowakowski@imgtec.com> Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/14336/ Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
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@ -866,3 +866,37 @@ int __compute_return_epc(struct pt_regs *regs)
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force_sig(SIGBUS, current);
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return -EFAULT;
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}
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#if (defined CONFIG_KPROBES) || (defined CONFIG_UPROBES)
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int __insn_is_compact_branch(union mips_instruction insn)
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{
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if (!cpu_has_mips_r6)
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return 0;
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switch (insn.i_format.opcode) {
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case blezl_op:
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case bgtzl_op:
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case blez_op:
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case bgtz_op:
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/*
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* blez[l] and bgtz[l] opcodes with non-zero rt
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* are MIPS R6 compact branches
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*/
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if (insn.i_format.rt)
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return 1;
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break;
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case bc6_op:
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case balc6_op:
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case pop10_op:
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case pop30_op:
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case pop66_op:
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case pop76_op:
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return 1;
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}
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return 0;
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}
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EXPORT_SYMBOL_GPL(__insn_is_compact_branch);
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#endif /* CONFIG_KPROBES || CONFIG_UPROBES */
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@ -106,6 +106,12 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
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goto out;
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}
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if (__insn_is_compact_branch(insn)) {
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pr_notice("Kprobes for compact branches are not supported\n");
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ret = -EINVAL;
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goto out;
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}
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/* insn: must be on special executable page on mips. */
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p->ainsn.insn = get_insn_slot();
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if (!p->ainsn.insn) {
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@ -13,6 +13,8 @@
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#include <asm/inst.h>
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int __insn_is_compact_branch(union mips_instruction insn);
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static inline int __insn_has_delay_slot(const union mips_instruction insn)
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{
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switch (insn.i_format.opcode) {
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@ -36,6 +36,12 @@ int arch_uprobe_analyze_insn(struct arch_uprobe *aup,
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return -EINVAL;
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inst.word = aup->insn[0];
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if (__insn_is_compact_branch(inst)) {
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pr_notice("Uprobes for compact branches are not supported\n");
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return -EINVAL;
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}
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aup->ixol[0] = aup->insn[insn_has_delay_slot(inst)];
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aup->ixol[1] = UPROBE_BRK_UPROBE_XOL; /* NOP */
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