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dbcd7f5faf
Inspired by commit 800834285361("bpf, arm64: Add BPF exception tables"),
do similar to LoongArch to add BPF exception tables.
When a tracing BPF program attempts to read memory without using the
bpf_probe_read() helper, the verifier marks the load instruction with
the BPF_PROBE_MEM flag. Since the LoongArch JIT does not currently
recognize this flag it falls back to the interpreter.
Add support for BPF_PROBE_MEM, by appending an exception table to the
BPF program. If the load instruction causes a data abort, the fixup
infrastructure finds the exception table and fixes up the fault, by
clearing the destination register and jumping over the faulting
instruction.
To keep the compact exception table entry format, inspect the pc in
fixup_exception(). A more generic solution would add a "handler" field
to the table entry, like on x86, s390 and arm64, etc.
Signed-off-by: Youling Tang <tangyouling@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
63 lines
1.5 KiB
C
63 lines
1.5 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Copyright (C) 2020-2022 Loongson Technology Corporation Limited
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*/
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#include <linux/bitfield.h>
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#include <linux/extable.h>
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#include <linux/uaccess.h>
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#include <asm/asm-extable.h>
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#include <asm/branch.h>
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static inline unsigned long
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get_ex_fixup(const struct exception_table_entry *ex)
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{
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return ((unsigned long)&ex->fixup + ex->fixup);
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}
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static inline void regs_set_gpr(struct pt_regs *regs,
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unsigned int offset, unsigned long val)
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{
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if (offset && offset <= MAX_REG_OFFSET)
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*(unsigned long *)((unsigned long)regs + offset) = val;
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}
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static bool ex_handler_fixup(const struct exception_table_entry *ex,
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struct pt_regs *regs)
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{
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regs->csr_era = get_ex_fixup(ex);
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return true;
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}
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static bool ex_handler_uaccess_err_zero(const struct exception_table_entry *ex,
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struct pt_regs *regs)
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{
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int reg_err = FIELD_GET(EX_DATA_REG_ERR, ex->data);
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int reg_zero = FIELD_GET(EX_DATA_REG_ZERO, ex->data);
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regs_set_gpr(regs, reg_err * sizeof(unsigned long), -EFAULT);
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regs_set_gpr(regs, reg_zero * sizeof(unsigned long), 0);
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regs->csr_era = get_ex_fixup(ex);
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return true;
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}
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bool fixup_exception(struct pt_regs *regs)
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{
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const struct exception_table_entry *ex;
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ex = search_exception_tables(exception_era(regs));
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if (!ex)
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return false;
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switch (ex->type) {
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case EX_TYPE_FIXUP:
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return ex_handler_fixup(ex, regs);
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case EX_TYPE_UACCESS_ERR_ZERO:
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return ex_handler_uaccess_err_zero(ex, regs);
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case EX_TYPE_BPF:
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return ex_handler_bpf(ex, regs);
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}
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BUG();
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}
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