Messages in this thread | | | Date | Mon, 30 Nov 2020 14:44:42 +0100 | From | Borislav Petkov <> | Subject | Re: [RFC PATCH v0 00/19] x86/insn: Add an insn_decode() API |
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On Sun, Nov 29, 2020 at 05:50:05PM +0900, Masami Hiramatsu wrote: > Good point. I think we can return, e.g. -EFAULT if we failed in > get_next(). Then, we can read out next page, for example.
Why -EFAULT?
Running this
size = 1; ret = insn_decode(&insn, b, size, INSN_MODE_64)
i.e., buffer size is 1:
./arch/x86/tools/insn_sanity: Success: decoded and checked 10000 random instructions with 0 errors (seed:0x9994a137) insn buffer: 0x48 0xcf 0x48 0x83 0x90 0x90 0x90 0x90 0x90 0x90 0x90 0x90 0x90 0x90 0x90 supplied buf size: 15, ret 0 supplied buf size: 2, ret 0 supplied buf size: 3, ret 0 supplied buf size: 4, ret 0 insn_decode: entry insn_decode: will get_length insn_get_immediate: getting immediate insn_get_displacement: getting displacement insn_get_sib: getting sib insn_get_modrm: entry insn_get_opcode: entry insn_get_prefixes: entry, prefixes->got: 0 insn_get_prefixes: 1 insn_get_prefixes: REX insn_get_prefixes: VEX insn_get_prefixes: validate_next: 0 insn_get_prefixes: insn->next_byte: 0x7ffec297c3e1, insn->end_kaddr: 0x7ffec297c3e1 insn_get_prefixes: errored out supplied buf size: 1, ret -22
is caught in validate_next() where ->next_byte == ->end_kaddr.
I'm thinking we should return EOF here, to denote that we're reached the end and then propagate that error up the callchain.
We don't have "define EOF" in the kernel but we can designate one for the insn decoder, perhaps
#define EOF -1
as stdio.h does:
/* The value returned by fgetc and similar functions to indicate the end of the file. */ #define EOF (-1)
Hmm, but then the callers would need to know EOF too so maybe EIO or something.
In any case, it should be a value which callers should be able to use to get told that input buffer is truncated...
Thx.
-- Regards/Gruss, Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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