linux-kernel - Re: [PATCH 0/8] smb: client: More crypto library conversions

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Message-ID: <20251014034230.GC2763@sol>
Date: Mon, 13 Oct 2025 20:42:30 -0700
From: Eric Biggers <ebiggers@...nel.org>
To: linux-cifs@...r.kernel.org, Steve French <sfrench@...ba.org>
Cc: samba-technical@...ts.samba.org, linux-crypto@...r.kernel.org,
	linux-kernel@...r.kernel.org, Paulo Alcantara <pc@...guebit.org>,
	Ronnie Sahlberg <ronniesahlberg@...il.com>,
	Shyam Prasad N <sprasad@...rosoft.com>, Tom Talpey <tom@...pey.com>,
	Bharath SM <bharathsm@...rosoft.com>
Subject: Re: [PATCH 0/8] smb: client: More crypto library conversions

On Sat, Oct 11, 2025 at 06:57:30PM -0700, Eric Biggers wrote:
> This series converts fs/smb/client/ to access SHA-512, HMAC-SHA256, MD5,
> and HMAC-MD5 using the library APIs instead of crypto_shash.
> 
> This simplifies the code significantly.  It also slightly improves
> performance, as it eliminates unnecessary overhead.
> 
> Tested with Samba with all SMB versions, with mfsymlinks in the mount
> options, 'server min protocol = NT1' and 'server signing = required' in
> smb.conf, and doing a simple file data and symlink verification test.
> That seems to cover all the modified code paths.
> 
> However, with SMB 1.0 I get "CIFS: VFS: SMB signature verification
> returned error = -13", regardless of whether this series is applied or
> not.  Presumably, testing that case requires some other setting I
> couldn't find.
> 
> Regardless, these are straightforward conversions and all the actual
> crypto is exactly the same as before, as far as I can tell.
> 
> Eric Biggers (8):
>   smb: client: Use SHA-512 library for SMB3.1.1 preauth hash
>   smb: client: Use HMAC-SHA256 library for key generation
>   smb: client: Use HMAC-SHA256 library for SMB2 signature calculation
>   smb: client: Use MD5 library for M-F symlink hashing
>   smb: client: Use MD5 library for SMB1 signature calculation
>   smb: client: Use HMAC-MD5 library for NTLMv2
>   smb: client: Remove obsolete crypto_shash allocations
>   smb: client: Consolidate cmac(aes) shash allocation

As requested off-list, here are some (micro)benchmark results for this
series.  The CPU was AMD Ryzen 9 9950X.  The server was Samba running on
localhost.  Message signing was enabled.  A valid username and password
were given in the mount options.  The "Improvement" column is the
percent change in throughput (reciprocal cycles):

           Microbenchmark               Before      After   Improvement
           ==============               ======      =====   ===========

    1. Total cycles spent in             44548      20081      122%
    smb311_update_preauth_hash()
    during SMB 3.1.1 mount
    (4 calls total)

    2. setup_ntlmv2_rsp() cycles         31777      22231       43%

    3. Total cycles spent in             17802      22876      -22%
    generate_key()
    during SMB 3.1.1 mount
    (3 calls total)

    4. Total cycles spent in            205110      87204      135%
    smb2_calc_signature()
    during SMB 2.0 mount
    (26 calls & 3316 bytes total)

    5. Total cycles spent in          22689767   21043125        8%
    smb2_calc_signature()
    reading 10MB file using SMB 2.0
    (316 calls & 10031077 bytes total)

    6. Total cycles spent in             56803      37840       50%
    cifs_calc_signature()
    during SMB 1.0 mount
    (18 calls & 1551 bytes total)

    7. Total cycles spent in          52669066   51974573        1%
    cifs_calc_signature()
    reading 10MB file using SMB 1.0
    (336 calls & 10021426 bytes total)

    8. parse_mf_symlink() cycles          7654       4902       56%

Note: case 3 regressed because the "cmac(aes)" allocation moved from
smb311_update_preauth_hash (case 1) to generate_key (case 3).  Excluding
that allocation, generate_key got faster.  Likewise, the sum of cases 1,
2, and 3 (which all occurred at mount time) got faster.

There was a greater speedup in signature calculation than I expected.
It's probably because many SMB messages are short (especially the ones
exchanged at mount time), and also because the old code allocated new
crypto_shash objects more frequently than I had thought.  The SMB 2.0
code allocated a new "hmac(sha256)" crypto_shash for every other message
signed.  That overhead is all gone after switching to the library.

TLDR: all SMB crypto calculations (SHA-512, HMAC-SHA256, MD5, HMAC-MD5)
affected by this series are faster now.  The library APIs fix the
unnecessary overhead that the traditional crypto API has.  Of course,
it's also a lot easier to use as well.

- Eric