Re: [v6 PATCH 04/21] x86/mpx, x86/insn: Relocate insn util functions to a new insn-kernel

Borislav Petkov
2017-04-12T10:03:08Z

On Tue, Mar 07, 2017 at 04:32:37PM -0800, Ricardo Neri wrote:
> Other kernel submodules can benefit from using the utility functions
> defined in mpx.c to obtain the addresses and values of operands contained
> in the general purpose registers. An instance of this is the emulation code
> used for instructions protected by the Intel User-Mode Instruction
> Prevention feature.
>
> Thus, these functions are relocated to a new insn-eval.c file. The reason
> to not relocate these utilities into insn.c is that the latter solely
> analyses instructions given by a struct insn without any knowledge of the
> meaning of the values of instruction operands. This new utility insn-
> eval.c aims to be used to resolve effective and userspace linear addresses
> based on the contents of the instruction operands as well as the contents
> of pt_regs structure.
>
> These utilities come with a separate header. This is to avoid taking insn.c
> out of sync from the instructions decoders under tools/obj and tools/perf.
> This also avoids adding cumbersome #ifdef's for the #include'd files
> required to decode instructions in a kernel context.
>
> Functions are simply relocated. There are not functional or indentation
> changes.

...

> + case REG_TYPE_BASE:
> + regno = X86_SIB_BASE(insn->sib.value);
> + /*
> + * If mod is 0 and register R/EBP (regno=5) is indicated in the
> + * base part of the SIB byte, the value of such register should
> + * not be used in the address computation. Also, a 32-bit
> + * displacement is expected in this case; the instruction
> + * decoder takes care of it. This is true for both R13 and
> + * R/EBP as REX.B will not be decoded.
> + */
> + if (regno == 5 && X86_MODRM_MOD(insn->modrm.value) == 0)
> + return -EDOM;
> +
> + if (X86_REX_B(insn->rex_prefix.value))
> + regno += 8;
> + break;
> +
> + default:
> + pr_err("invalid register type");
> + BUG();

WARNING: Avoid crashing the kernel - try using WARN_ON & recovery code rather than BUG() or BUG_ON()
#211: FILE: arch/x86/lib/insn-eval.c:90:
+ BUG();

And checkpatch is kinda right. We need to warn here, not explode. Oh and
that function returns negative values on error...

Please change that with a patch ontop of the move.

Thanks.

--
Regards/Gruss,
Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
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