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Wed, 12 Aug 2026 01:13:53 -0700 (PDT) Message-ID: Date: Wed, 12 Aug 2026 10:13:51 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v8 6/7] xen/serial: harden serial_tx_buffer checks To: Stefano Stabellini , dmukhin@ford.com Cc: xen-devel@lists.xenproject.org, andrew.cooper3@citrix.com, anthony.perard@vates.tech, julien@xen.org, michal.orzel@amd.com, =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= References: <20260728065049.1318143-1-dmukhin@ford.com> <20260728065049.1318143-7-dmukhin@ford.com> <4b040e58-9020-a519-00cb-816ce2fddaa0@kernel.org> Content-Language: en-US From: Jan Beulich Autocrypt: addr=jbeulich@suse.com; keydata= xsDiBFk3nEQRBADAEaSw6zC/EJkiwGPXbWtPxl2xCdSoeepS07jW8UgcHNurfHvUzogEq5xk hu507c3BarVjyWCJOylMNR98Yd8VqD9UfmX0Hb8/BrA+Hl6/DB/eqGptrf4BSRwcZQM32aZK 7Pj2XbGWIUrZrd70x1eAP9QE3P79Y2oLrsCgbZJfEwCgvz9JjGmQqQkRiTVzlZVCJYcyGGsD /0tbFCzD2h20ahe8rC1gbb3K3qk+LpBtvjBu1RY9drYk0NymiGbJWZgab6t1jM7sk2vuf0Py O9Hf9XBmK0uE9IgMaiCpc32XV9oASz6UJebwkX+zF2jG5I1BfnO9g7KlotcA/v5ClMjgo6Gl MDY4HxoSRu3i1cqqSDtVlt+AOVBJBACrZcnHAUSuCXBPy0jOlBhxPqRWv6ND4c9PH1xjQ3NP nxJuMBS8rnNg22uyfAgmBKNLpLgAGVRMZGaGoJObGf72s6TeIqKJo/LtggAS9qAUiuKVnygo 3wjfkS9A3DRO+SpU7JqWdsveeIQyeyEJ/8PTowmSQLakF+3fote9ybzd880fSmFuIEJldWxp Y2ggPGpiZXVsaWNoQHN1c2UuY29tPsJgBBMRAgAgBQJZN5xEAhsDBgsJCAcDAgQVAggDBBYC AwECHgECF4AACgkQoDSui/t3IH4J+wCfQ5jHdEjCRHj23O/5ttg9r9OIruwAn3103WUITZee e7Sbg12UgcQ5lv7SzsFNBFk3nEQQCACCuTjCjFOUdi5Nm244F+78kLghRcin/awv+IrTcIWF hUpSs1Y91iQQ7KItirz5uwCPlwejSJDQJLIS+QtJHaXDXeV6NI0Uef1hP20+y8qydDiVkv6l IreXjTb7DvksRgJNvCkWtYnlS3mYvQ9NzS9PhyALWbXnH6sIJd2O9lKS1Mrfq+y0IXCP10eS FFGg+Av3IQeFatkJAyju0PPthyTqxSI4lZYuJVPknzgaeuJv/2NccrPvmeDg6Coe7ZIeQ8Yj t0ARxu2xytAkkLCel1Lz1WLmwLstV30g80nkgZf/wr+/BXJW/oIvRlonUkxv+IbBM3dX2OV8 AmRv1ySWPTP7AAMFB/9PQK/VtlNUJvg8GXj9ootzrteGfVZVVT4XBJkfwBcpC/XcPzldjv+3 HYudvpdNK3lLujXeA5fLOH+Z/G9WBc5pFVSMocI71I8bT8lIAzreg0WvkWg5V2WZsUMlnDL9 mpwIGFhlbM3gfDMs7MPMu8YQRFVdUvtSpaAs8OFfGQ0ia3LGZcjA6Ik2+xcqscEJzNH+qh8V m5jjp28yZgaqTaRbg3M/+MTbMpicpZuqF4rnB0AQD12/3BNWDR6bmh+EkYSMcEIpQmBM51qM EKYTQGybRCjpnKHGOxG0rfFY1085mBDZCH5Kx0cl0HVJuQKC+dV2ZY5AqjcKwAxpE75MLFkr wkkEGBECAAkFAlk3nEQCGwwACgkQoDSui/t3IH7nnwCfcJWUDUFKdCsBH/E5d+0ZnMQi+G0A nAuWpQkjM1ASeQwSHEeAWPgskBQL In-Reply-To: <4b040e58-9020-a519-00cb-816ce2fddaa0@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-purgate-ID: tlsNG-c1860d/1786522433-D735D87B-FB6483E6/0/0 X-purgate-type: clean X-purgate-size: 1186 On 10.08.2026 22:32, Stefano Stabellini wrote: > On Mon, 27 Jul 2026, dmukhin@ford.com wrote: >> --- a/xen/drivers/char/serial.c >> +++ b/xen/drivers/char/serial.c >> @@ -523,6 +523,8 @@ void __init serial_async_transmit(struct serial_port *port) >> return; >> if ( serial_txbufsz < PAGE_SIZE ) >> serial_txbufsz = PAGE_SIZE; >> + if ( serial_txbufsz > GB(2) ) >> + serial_txbufsz = CONFIG_SERIAL_TX_BUFSIZE; >> while ( serial_txbufsz & (serial_txbufsz - 1) ) >> serial_txbufsz &= serial_txbufsz - 1; > > My understanding of this loop is that, given that serial_txbufsz is > unsigned int, it is already clamping it to 2GB max It would, yes, as long as sizeof(unsigned int) == sizeof(uint32_t). While we certainly have many instances of that assumption in the code, I think we're well advised to avoid adding more. Furthermore (see related comments on patch 5) one may raise the question whether serial_txbufsz wouldn't better be of type size_t. What I'm uncertain about is the resetting to CONFIG_SERIAL_TX_BUFSIZE here: When an overly huge size was requested, shouldn't we give the biggest we permit? Jan