linux-kernel - Re: [PATCH v2 2/5] x86/tdx: Add validation of userspace MMIO instructions

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Message-ID: <83c9b05e7d359c0486a061f3bd31920ddb5c33a0.camel@intel.com>
Date: Mon, 5 Aug 2024 22:40:55 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "linux-coco@...ts.linux.dev" <linux-coco@...ts.linux.dev>,
	"legion@...nel.org" <legion@...nel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
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	<kai.huang@...el.com>, "Yao, Yuan" <yuan.yao@...el.com>,
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Subject: Re: [PATCH v2 2/5] x86/tdx: Add validation of userspace MMIO
 instructions

On Mon, 2024-08-05 at 15:29 +0200, Alexey Gladkov (Intel) wrote:
> +       vaddr = (unsigned long)insn_get_addr_ref(&insn, regs);
> +
> +       if (user_mode(regs)) {
> +               if (mmap_read_lock_killable(current->mm))
> +                       return -EINTR;
> +
> +               ret = valid_vaddr(ve, mmio, size, vaddr);
> +               if (ret)
> +                       goto unlock;
> +       }
> +

In the case of user MMIO, if the user instruction + MAX_INSN_SIZE straddles a
page, then the "fetch" in the kernel could trigger a #VE. In this case the  
kernel would handle this second #VE as a !user_mode() MMIO I guess.

Would something prevent the same munmap() checks needing to happen for that
second kernel #VE? If not, I wonder if the munmap() protection logic should also
trigger for any userspace range ve->gpa as well.