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[2001:8b0:1d0::2]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3663a2f698dsm4393006f8f.70.2024.06.22.05.06.52 for (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 22 Jun 2024 05:06:52 -0700 (PDT) From: Peter Maydell To: qemu-devel@nongnu.org Subject: [PULL 17/18] hw/usb/hcd-ohci: Fix ohci_service_td: accept zero-length TDs where CBP=BE+1 Date: Sat, 22 Jun 2024 13:06:42 +0100 Message-Id: <20240622120643.3797539-18-peter.maydell@linaro.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20240622120643.3797539-1-peter.maydell@linaro.org> References: <20240622120643.3797539-1-peter.maydell@linaro.org> MIME-Version: 1.0 Received-SPF: pass client-ip=2a00:1450:4864:20::42d; envelope-from=peter.maydell@linaro.org; helo=mail-wr1-x42d.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, 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: 2.1.29 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-bounces+qemu-devel=archiver.kernel.org@nongnu.org From: David Hubbard This changes the way the ohci emulation handles a Transfer Descriptor with "Buffer End" set to "Current Buffer Pointer" - 1, specifically in the case of a zero-length packet. The OHCI spec 4.3.1.2 Table 4-2 specifies td.cbp to be zero for a zero-length packet. Peter Maydell tracked down commit 1328fe0c32 (hw: usb: hcd-ohci: check len and frame_number variables) where qemu started checking this according to the spec. What this patch does is loosen the qemu ohci implementation to allow a zero-length packet if td.be (Buffer End) is set to td.cbp - 1, and with a non-zero td.cbp value. The spec is unclear whether this is valid or not -- it is not the clearly documented way to send a zero length TD (which is CBP=BE=0), but it isn't specifically forbidden. Actual hw seems to be ok with it. Does any OS rely on this behavior? There have been no reports to qemu-devel of this problem. This is attempting to have qemu behave like actual hardware, but this is just a minor change. With a tiny OS[1] that boots and executes a test, the issue can be seen: * OS that sends USB requests to a USB mass storage device but sends td.cbp = td.be + 1 * qemu 4.2 * qemu HEAD (4e66a0854) * Actual OHCI controller (hardware) Command line: qemu-system-x86_64 -m 20 \ -device pci-ohci,id=ohci \ -drive if=none,format=raw,id=d,file=testmbr.raw \ -device usb-storage,bus=ohci.0,drive=d \ --trace "usb_*" --trace "ohci_*" -D qemu.log Results are: qemu 4.2 | qemu HEAD | actual HW -----------+------------+----------- works fine | ohci_die() | works fine Tip: if the flags "-serial pty -serial stdio" are added to the command line the test will output USB requests like this: Testing qemu HEAD: > Free mem 2M ohci port2 conn FS > setup { 80 6 0 1 0 0 8 0 } > ED info=80000 { mps=8 en=0 d=0 } tail=c20920 > td0 c20880 nxt=c20960 f2000000 setup cbp=c20900 be=c20907 > td1 c20960 nxt=c20980 f3140000 in cbp=c20908 be=c2090f > td2 c20980 nxt=c20920 f3080000 out cbp=c20910 be=c2090f ohci20 host err > usb stopped And in qemu.log: usb_ohci_iso_td_bad_cc_overrun ISO_TD start_offset=0x00c20910 > next_offset=0x00c2090f Testing qemu 4.2: > Free mem 2M ohci port2 conn FS > setup { 80 6 0 1 0 0 8 0 } > ED info=80000 { mps=8 en=0 d=0 } tail=620920 > td0 620880 nxt=620960 f2000000 setup cbp=620900 be=620907 cbp=0 be=620907 > td1 620960 nxt=620980 f3140000 in cbp=620908 be=62090f cbp=0 be=62090f > td2 620980 nxt=620920 f3080000 out cbp=620910 be=62090f cbp=0 be=62090f > rx { 12 1 0 2 0 0 0 8 } > setup { 0 5 1 0 0 0 0 0 } tx {} > ED info=80000 { mps=8 en=0 d=0 } tail=620880 > td0 620920 nxt=620960 f2000000 setup cbp=620900 be=620907 cbp=0 be=620907 > td1 620960 nxt=620880 f3100000 in cbp=620908 be=620907 cbp=0 be=620907 > setup { 80 6 0 1 0 0 12 0 } > ED info=80001 { mps=8 en=0 d=1 } tail=620960 > td0 620880 nxt=6209c0 f2000000 setup cbp=620920 be=620927 cbp=0 be=620927 > td1 6209c0 nxt=6209e0 f3140000 in cbp=620928 be=620939 cbp=0 be=620939 > td2 6209e0 nxt=620960 f3080000 out cbp=62093a be=620939 cbp=0 be=620939 > rx { 12 1 0 2 0 0 0 8 f4 46 1 0 0 0 1 2 3 1 } > setup { 80 6 0 2 0 0 0 1 } > ED info=80001 { mps=8 en=0 d=1 } tail=620880 > td0 620960 nxt=6209a0 f2000000 setup cbp=620a20 be=620a27 cbp=0 be=620a27 > td1 6209a0 nxt=6209c0 f3140004 in cbp=620a28 be=620b27 cbp=620a48 be=620b27 > td2 6209c0 nxt=620880 f3080000 out cbp=620b28 be=620b27 cbp=0 be=620b27 > rx { 9 2 20 0 1 1 4 c0 0 9 4 0 0 2 8 6 50 0 7 5 81 2 40 0 0 7 5 2 2 40 0 0 } > setup { 0 9 1 0 0 0 0 0 } tx {} > ED info=80001 { mps=8 en=0 d=1 } tail=620900 > td0 620880 nxt=620940 f2000000 setup cbp=620a00 be=620a07 cbp=0 be=620a07 > td1 620940 nxt=620900 f3100000 in cbp=620a08 be=620a07 cbp=0 be=620a07 [1] The OS disk image has been emailed to philmd@linaro.org, mjt@tls.msk.ru, and kraxel@redhat.com: * testCbpOffBy1.img.xz * sha256: f87baddcb86de845de12f002c698670a426affb40946025cc32694f9daa3abed Signed-off-by: David Hubbard Reviewed-by: Alex Bennée Reviewed-by: Peter Maydell Signed-off-by: Peter Maydell --- hw/usb/hcd-ohci.c | 4 ++-- hw/usb/trace-events | 1 + 2 files changed, 3 insertions(+), 2 deletions(-) diff --git a/hw/usb/hcd-ohci.c b/hw/usb/hcd-ohci.c index acd60169802..71b54914d32 100644 --- a/hw/usb/hcd-ohci.c +++ b/hw/usb/hcd-ohci.c @@ -941,8 +941,8 @@ static int ohci_service_td(OHCIState *ohci, struct ohci_ed *ed) if ((td.cbp & 0xfffff000) != (td.be & 0xfffff000)) { len = (td.be & 0xfff) + 0x1001 - (td.cbp & 0xfff); } else { - if (td.cbp > td.be) { - trace_usb_ohci_iso_td_bad_cc_overrun(td.cbp, td.be); + if (td.cbp - 1 > td.be) { /* rely on td.cbp != 0 */ + trace_usb_ohci_td_bad_buf(td.cbp, td.be); ohci_die(ohci); return 1; } diff --git a/hw/usb/trace-events b/hw/usb/trace-events index 46732717a95..dd04f14add1 100644 --- a/hw/usb/trace-events +++ b/hw/usb/trace-events @@ -29,6 +29,7 @@ usb_ohci_iso_td_data_underrun(int ret) "DataUnderrun %d" usb_ohci_iso_td_nak(int ret) "got NAK/STALL %d" usb_ohci_iso_td_bad_response(int ret) "Bad device response %d" usb_ohci_td_bad_pid(const char *s, uint32_t edf, uint32_t tdf) "Bad pid %s: ed.flags 0x%x td.flags 0x%x" +usb_ohci_td_bad_buf(uint32_t cbp, uint32_t be) "Bad cbp = 0x%x > be = 0x%x" usb_ohci_port_attach(int index) "port #%d" usb_ohci_port_detach(int index) "port #%d" usb_ohci_port_wakeup(int index) "port #%d"