linux-kernel - Re: [PATCH v38 17/24] x86/sgx: ptrace() support for the SGX driver

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Date:   Tue, 22 Sep 2020 17:44:24 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     x86@...nel.org, linux-sgx@...r.kernel.org,
        linux-kernel@...r.kernel.org, Jethro Beekman <jethro@...tanix.com>,
        akpm@...ux-foundation.org, andriy.shevchenko@...ux.intel.com,
        asapek@...gle.com, cedric.xing@...el.com, chenalexchen@...gle.com,
        conradparker@...gle.com, cyhanish@...gle.com,
        dave.hansen@...el.com, haitao.huang@...el.com,
        josh@...htriplett.org, kai.huang@...el.com, kai.svahn@...el.com,
        kmoy@...gle.com, ludloff@...gle.com, luto@...nel.org,
        nhorman@...hat.com, npmccallum@...hat.com, puiterwijk@...hat.com,
        rientjes@...gle.com, sean.j.christopherson@...el.com,
        tglx@...utronix.de, yaozhangx@...gle.com
Subject: Re: [PATCH v38 17/24] x86/sgx: ptrace() support for the SGX driver


> Subject: Re: [PATCH v38 17/24] x86/sgx: ptrace() support for the SGX driver
			     ... x86/sgx: Add ptrace() support...

subject needs a verb.

On Tue, Sep 15, 2020 at 02:28:35PM +0300, Jarkko Sakkinen wrote:
> Add VMA callbacks for ptrace() that can be used with debug enclaves.
> With debug enclaves data can be read and write the memory word at a time

I think you wanna say here

"... data can be read and/or written a memory word at a time by using..."

> by using ENCLS(EDBGRD) and ENCLS(EDBGWR) leaf instructions.
> 
> Acked-by: Jethro Beekman <jethro@...tanix.com>
> Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
> ---
>  arch/x86/kernel/cpu/sgx/encl.c | 87 ++++++++++++++++++++++++++++++++++
>  1 file changed, 87 insertions(+)
> 
> diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c
> index 11ec2df59b54..7f8df2c8ef35 100644
> --- a/arch/x86/kernel/cpu/sgx/encl.c
> +++ b/arch/x86/kernel/cpu/sgx/encl.c
> @@ -333,10 +333,97 @@ static int sgx_vma_mprotect(struct vm_area_struct *vma,
>  	return mprotect_fixup(vma, pprev, start, end, newflags);
>  }
>  
> +static int sgx_edbgrd(struct sgx_encl *encl, struct sgx_encl_page *page,
> +		      unsigned long addr, void *data)
> +{
> +	unsigned long offset = addr & ~PAGE_MASK;
> +	int ret;
> +
> +
> +	ret = __edbgrd(sgx_get_epc_addr(page->epc_page) + offset, data);
> +	if (ret)
> +		return -EIO;
> +
> +	return 0;
> +}
> +
> +static int sgx_edbgwr(struct sgx_encl *encl, struct sgx_encl_page *page,
> +		      unsigned long addr, void *data)
> +{
> +	unsigned long offset = addr & ~PAGE_MASK;
> +	int ret;
> +
> +	ret = __edbgwr(sgx_get_epc_addr(page->epc_page) + offset, data);
> +	if (ret)
> +		return -EIO;
> +
> +	return 0;
> +}

I know those are supposed to correspond to the ENCLS leafs but the
function names are totally unreadable. I guess you could name them

sgx_encl_dbg_read
sgx_encl_dbg_write

and leave the lowlevel helpers like the insn names.

> +static int sgx_vma_access(struct vm_area_struct *vma, unsigned long addr,
> +			  void *buf, int len, int write)
> +{
> +	struct sgx_encl *encl = vma->vm_private_data;
> +	struct sgx_encl_page *entry = NULL;
> +	char data[sizeof(unsigned long)];
> +	unsigned long align;
> +	unsigned int flags;
> +	int offset;
> +	int cnt;
> +	int ret = 0;
> +	int i;
> +
> +	/* If process was forked, VMA is still there but vm_private_data is set
> +	 * to NULL.
> +	 */

Kernel comments style is:

	/*
	 * A sentence ending with a full-stop.
	 * Another sentence. ...
	 * More sentences. ...
	 */

> +	if (!encl)
> +		return -EFAULT;
> +
> +	flags = atomic_read(&encl->flags);
> +
> +	if (!(flags & SGX_ENCL_DEBUG) || !(flags & SGX_ENCL_INITIALIZED) ||
> +	    (flags & SGX_ENCL_DEAD))
> +		return -EFAULT;
> +
> +	for (i = 0; i < len; i += cnt) {
> +		entry = sgx_encl_reserve_page(encl, (addr + i) & PAGE_MASK);
> +		if (IS_ERR(entry)) {
> +			ret = PTR_ERR(entry);
> +			break;
> +		}
> +
> +		align = ALIGN_DOWN(addr + i, sizeof(unsigned long));
> +		offset = (addr + i) & (sizeof(unsigned long) - 1);
> +		cnt = sizeof(unsigned long) - offset;
> +		cnt = min(cnt, len - i);
> +
> +		ret = sgx_edbgrd(encl, entry, align, data);
> +		if (ret)
> +			goto out;
> +
> +		if (write) {
> +			memcpy(data + offset, buf + i, cnt);
> +			ret = sgx_edbgwr(encl, entry, align, data);
> +			if (ret)
> +				goto out;
> +		} else

		} else {

> +			memcpy(buf + i, data + offset, cnt);

		}

Put the else branch in {} too.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette