linux-kernel - Re: [PATCH v8 09/28] x86/insn-eval: Do not BUG on invalid register type

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Date:   Thu, 7 Sep 2017 19:54:14 +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>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Shuah Khan <shuah@...nel.org>, linux-kernel@...r.kernel.org,
        x86@...nel.org, ricardo.neri@...el.com,
        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: [PATCH v8 09/28] x86/insn-eval: Do not BUG on invalid register
 type

On Fri, Aug 18, 2017 at 05:27:50PM -0700, Ricardo Neri wrote:
> We are not in a critical failure path. The invalid register type is caused
> when trying to decode invalid instruction bytes from a user-space program.
> Thus, simply print an error message. To prevent this warning from being
> abused from user space programs, use the rate-limited variant of pr_err().
> 
> Cc: Borislav Petkov <bp@...e.de>
> Cc: Andy Lutomirski <luto@...nel.org>
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: Adam Buchbinder <adam.buchbinder@...il.com>
> Cc: Colin Ian King <colin.king@...onical.com>
> Cc: Lorenzo Stoakes <lstoakes@...il.com>
> Cc: Qiaowei Ren <qiaowei.ren@...el.com>
> Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
> Cc: Masami Hiramatsu <mhiramat@...nel.org>
> Cc: Adrian Hunter <adrian.hunter@...el.com>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Thomas Garnier <thgarnie@...gle.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Dmitry Vyukov <dvyukov@...gle.com>
> Cc: Ravi V. Shankar <ravi.v.shankar@...el.com>
> Cc: x86@...nel.org
> Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
> ---
>  arch/x86/lib/insn-eval.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
> index 2bb8303ba92f..3919458fecbf 100644
> --- a/arch/x86/lib/insn-eval.c
> +++ b/arch/x86/lib/insn-eval.c
> @@ -5,6 +5,7 @@
>   */
>  #include <linux/kernel.h>
>  #include <linux/string.h>
> +#include <linux/ratelimit.h>
>  #include <asm/inat.h>
>  #include <asm/insn.h>
>  #include <asm/insn-eval.h>
> @@ -85,9 +86,8 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs,
>  		break;
>  
>  	default:
> -		pr_err("invalid register type");
> -		BUG();
> -		break;
> +		pr_err_ratelimited("insn: x86: invalid register type");

Also, I meant to add it to pr_fmt. Feel free to merge this hunk ontop of
yours:

---
diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
index 3919458fecbf..d46034ddfbb7 100644
--- a/arch/x86/lib/insn-eval.c
+++ b/arch/x86/lib/insn-eval.c
@@ -10,6 +10,9 @@
 #include <asm/insn.h>
 #include <asm/insn-eval.h>
 
+#undef pr_fmt
+#define pr_fmt(fmt) "insn: " fmt
+
 enum reg_type {
 	REG_TYPE_RM = 0,
 	REG_TYPE_INDEX,
@@ -86,7 +89,7 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs,
 		break;
 
 	default:
-		pr_err_ratelimited("insn: x86: invalid register type");
+		pr_err_ratelimited("invalid register type: %d\n", type);
 		return -EINVAL;
 	}
 

-- 
Regards/Gruss,
    Boris.

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