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When generating instructions at runtime, for example due to kernel text patching or the BPF JIT, we can emit a trapping BRK instruction if we are asked to encode an invalid instruction such as an out-of-range] branch. This is indicative of a bug in the caller, and will result in a crash on executing the generated code. Unfortunately, the message from the crash is really unhelpful, and mumbles something about ptrace: | Unexpected kernel BRK exception at EL1 | Internal error: ptrace BRK handler: f2000100 [#1] SMP We can do better than this. Install a break handler for FAULT_BRK_IMM, which is the immediate used to encode the "I've been asked to generate an invalid instruction" error, and triage the faulting PC to determine whether or not the failure occurred in the BPF JIT. Link: https://lore.kernel.org/r/20200915141707.GB26439@willie-the-truck Reported-by: Ilias Apalodimas <ilias.apalodimas@linaro.org> Signed-off-by: Will Deacon <will@kernel.org>
23 lines
452 B
C
23 lines
452 B
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Based on arch/arm/mm/extable.c
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*/
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#include <linux/extable.h>
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#include <linux/uaccess.h>
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int fixup_exception(struct pt_regs *regs)
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{
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const struct exception_table_entry *fixup;
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fixup = search_exception_tables(instruction_pointer(regs));
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if (!fixup)
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return 0;
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if (in_bpf_jit(regs))
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return arm64_bpf_fixup_exception(fixup, regs);
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regs->pc = (unsigned long)&fixup->fixup + fixup->fixup;
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return 1;
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}
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