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

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Date:   Wed, 12 Apr 2017 12:03:08 +0200
From:   Borislav Petkov <bp@...e.de>
To:     Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Brian Gerst <brgerst@...il.com>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Huang Rui <ray.huang@....com>, Jiri Slaby <jslaby@...e.cz>,
        Jonathan Corbet <corbet@....net>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Chen Yucong <slaoub@...il.com>,
        Alexandre Julliard <julliard@...ehq.org>,
        Stas Sergeev <stsp@...t.ru>, Fenghua Yu <fenghua.yu@...el.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Shuah Khan <shuah@...nel.org>, linux-kernel@...r.kernel.org,
        x86@...nel.org, linux-msdos@...r.kernel.org, wine-devel@...ehq.org,
        Adam Buchbinder <adam.buchbinder@...il.com>,
        Colin Ian King <colin.king@...onical.com>,
        Lorenzo Stoakes <lstoakes@...il.com>,
        Qiaowei Ren <qiaowei.ren@...el.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Kees Cook <keescook@...omium.org>,
        Thomas Garnier <thgarnie@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [v6 PATCH 04/21] x86/mpx, x86/insn: Relocate insn util functions
 to a new insn-kernel

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)
--