linux-kernel - Re: [PATCH] x86/sgx: Remove unnecessary kmap() from sgx_ioc_enclave

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Date:   Fri, 26 Mar 2021 21:45:24 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     ira.weiny@...el.com
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, Sean Christopherson <seanjc@...gle.com>,
        Jethro Beekman <jethro@...tanix.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        linux-sgx@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/sgx: Remove unnecessary kmap() from
 sgx_ioc_enclave_init()

On Wed, Mar 24, 2021 at 11:22:46AM -0700, ira.weiny@...el.com wrote:
> From: Ira Weiny <ira.weiny@...el.com>
> 
> kmap is inefficient and is being replaced by kmap_local_page(), if
> possible.

Nit: just saying that something is inefficient is not enough. Always
should have something to back it up.

> That said, there is no readily apparent reason why initp_page needs to
> be allocated and kmap'ed() except that 'sigstruct' needs to be page
> aligned and 'token' 512 byte aligned.
> 
> Rather than change this kmap() to kmap_local_page() use kmalloc()
> instead because kmalloc() can gives this alignment when allocating
> PAGE_SIZE bytes.
> 
> Remove the alloc_page()/kmap() and replace with kmalloc(PAGE_SIZE, ...)
> to get a page aligned kernel address.
> 
> In addition add a comment to document the alignment requirements so that
> others don't attempt to 'fix' this again.

I'm a bit confused based on this commit message. Why is kmap_local_page()
better, and why kmalloc() is the ultimate choice of all three options?

> 
> Cc: Sean Christopherson <seanjc@...gle.com>
> Cc: Jethro Beekman <jethro@...tanix.com>
> Cc: Jarkko Sakkinen <jarkko@...nel.org>
> Cc: Dave Hansen <dave.hansen@...el.com>
> Signed-off-by: Ira Weiny <ira.weiny@...el.com>
 
/Jarkko