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Thu, 01 Apr 2021 09:52:08 +0100 To: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= , qemu-devel@nongnu.org, alxndr@bu.edu, laurent@vivier.eu, pbonzini@redhat.com References: <20210401074933.9923-1-mark.cave-ayland@ilande.co.uk> <20210401074933.9923-8-mark.cave-ayland@ilande.co.uk> <2c2f7f50-a4bd-916f-6c71-a61dd4b566e9@amsat.org> From: Mark Cave-Ayland Message-ID: <8cd25d29-6442-9d10-63cb-58d165e944f1@ilande.co.uk> Date: Thu, 1 Apr 2021 09:51:51 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.9.0 MIME-Version: 1.0 In-Reply-To: <2c2f7f50-a4bd-916f-6c71-a61dd4b566e9@amsat.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-SA-Exim-Connect-IP: 86.148.103.9 X-SA-Exim-Mail-From: mark.cave-ayland@ilande.co.uk Subject: Re: [PATCH v3 07/11] esp: don't underflow cmdfifo in do_cmd() X-SA-Exim-Version: 4.2.1 (built Wed, 08 May 2019 21:11:16 +0000) X-SA-Exim-Scanned: Yes (on mail.default.ilande.uk0.bigv.io) Received-SPF: pass client-ip=2001:41c9:1:41f::167; envelope-from=mark.cave-ayland@ilande.co.uk; helo=mail.default.ilande.uk0.bigv.io X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, NICE_REPLY_A=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 01/04/2021 09:19, Philippe Mathieu-Daudé wrote: > On 4/1/21 9:49 AM, Mark Cave-Ayland wrote: >> If the guest tries to execute a CDB when cmdfifo is not empty before the start >> of the message out phase then clearing the message out phase data will cause >> cmdfifo to underflow due to cmdfifo_cdb_offset being larger than the amount of >> data within. >> >> Since this can only occur by issuing deliberately incorrect instruction >> sequences, ensure that the maximum length of esp_fifo_pop_buf() is limited to >> the size of the data within cmdfifo. >> >> Buglink: https://bugs.launchpad.net/qemu/+bug/1909247 >> Signed-off-by: Mark Cave-Ayland >> --- >> hw/scsi/esp.c | 6 ++++-- >> 1 file changed, 4 insertions(+), 2 deletions(-) >> >> diff --git a/hw/scsi/esp.c b/hw/scsi/esp.c >> index 4decbbfc29..7f49522e1d 100644 >> --- a/hw/scsi/esp.c >> +++ b/hw/scsi/esp.c >> @@ -319,13 +319,15 @@ static void do_busid_cmd(ESPState *s, uint8_t busid) >> >> static void do_cmd(ESPState *s) >> { >> - uint8_t busid = fifo8_pop(&s->cmdfifo); >> + uint8_t busid = esp_fifo_pop(&s->cmdfifo); >> + int len; >> >> s->cmdfifo_cdb_offset--; >> >> /* Ignore extended messages for now */ >> if (s->cmdfifo_cdb_offset) { >> - esp_fifo_pop_buf(&s->cmdfifo, NULL, s->cmdfifo_cdb_offset); >> + len = MIN(s->cmdfifo_cdb_offset, fifo8_num_used(&s->cmdfifo)); > > Do we want to log(GUEST_ERRORS) this? Not for this case, since a guest OS may legitimately try a SDTR negotiation using extended messages which the ESP implementation currently ignores. >> + esp_fifo_pop_buf(&s->cmdfifo, NULL, len); >> s->cmdfifo_cdb_offset = 0; >> } >> >> > > Reviewed-by: Philippe Mathieu-Daudé ATB, Mark.