linux-kernel - Re: [PATCH v2] x86/traps: Enable UBSAN traps on x86

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Date: Sat, 1 Jun 2024 07:06:37 -0700
From: Kees Cook <kees@...nel.org>
To: Gatlin Newhouse <gatlin.newhouse@...il.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>, Marco Elver <elver@...gle.com>,
	Andrey Konovalov <andreyknvl@...il.com>,
	Andrey Ryabinin <ryabinin.a.a@...il.com>,
	Nathan Chancellor <nathan@...nel.org>,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rick Edgecombe <rick.p.edgecombe@...el.com>,
	Baoquan He <bhe@...hat.com>, Changbin Du <changbin.du@...wei.com>,
	Pengfei Xu <pengfei.xu@...el.com>,
	Josh Poimboeuf <jpoimboe@...nel.org>, Xin Li <xin3.li@...el.com>,
	Jason Gunthorpe <jgg@...pe.ca>, Tina Zhang <tina.zhang@...el.com>,
	Uros Bizjak <ubizjak@...il.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com,
	linux-hardening@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH v2] x86/traps: Enable UBSAN traps on x86

On Sat, Jun 01, 2024 at 03:10:05AM +0000, Gatlin Newhouse wrote:
> +void handle_ubsan_failure(struct pt_regs *regs, int insn)
> +{
> +	u32 type = 0;
> +
> +	if (insn == INSN_ASOP) {
> +		type = (*(u16 *)(regs->ip + LEN_ASOP + LEN_UD1));
> +		if ((type & 0xFF) == 0x40)
> +			type = (type >> 8) & 0xFF;
> +	} else {
> +		type = (*(u16 *)(regs->ip + LEN_UD1));
> +		if ((type & 0xFF) == 0x40)
> +			type = (type >> 8) & 0xFF;
> +	}

The if/else code is repeated, but the only difference is the offset to
read from. Also, if the 0x40 is absent, we likely don't want to report
anything. So, perhaps:

	u16 offset = LEN_UD1;
	u32 type;

	if (insn == INSN_ASOP)
		offset += INSN_ASOP;
	type = *(u16 *)(regs->ip + offset);
	if ((type & 0xFF) != 0x40)
		return;

	type = (type >> 8) & 0xFF;
	pr_crit("%s at %pS\n", report_ubsan_failure(regs, type), (void *)regs->ip);



-- 
Kees Cook