[v1] Misc HW patches for 2026-02-22

[PULL 19/20] net: mark struct udp_header as QEMU_PACKED

Philippe Mathieu-Daudé posted 20 patches 1 month, 2 weeks ago

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Maintainers: Richard Henderson <richard.henderson@linaro.org>, Laurent Vivier <laurent@vivier.eu>, Jiri Pirko <jiri@resnulli.us>, Jason Wang <jasowang@redhat.com>, "Michael S. Tsirkin" <mst@redhat.com>, Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>, Nicholas Piggin <npiggin@gmail.com>, Chinmay Rath <rathc@linux.ibm.com>, "Hervé Poussineau" <hpoussin@reactos.org>, Harsh Prateek Bora <harshpb@linux.ibm.com>, Artyom Tarasenko <atar4qemu@gmail.com>, Stefano Garzarella <sgarzare@redhat.com>, Eduardo Habkost <eduardo@habkost.net>, Marcel Apfelbaum <marcel.apfelbaum@gmail.com>, "Philippe Mathieu-Daudé" <philmd@linaro.org>, Yanan Wang <wangyanan55@huawei.com>, Zhao Liu <zhao1.liu@intel.com>, Dmitry Fleytman <dmitry.fleytman@gmail.com>, Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>

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[PULL 19/20] net: mark struct udp_header as QEMU_PACKED

Posted by Philippe Mathieu-Daudé 1 month, 2 weeks ago

From: Peter Maydell <peter.maydell@linaro.org>

The eth_header is not actually guaranteed to be aligned.  We attempt
to deal with this in some places such as net_checksum_calculate() by
using lduw_be_p() and so on to access the fields, but this is not
sufficient to be correct, because even accessing a byte member within
a misaligned struct is undefined behaviour.  The clang sanitizer will
emit an error like this if you run the sifive_u_mmc functional test
with sanitizers enabled:

../../net/checksum.c:168:24: runtime error: member access within misaligned address 0x5b7a7f829033 for type 'udp_header' (aka 'struct udp_header'), which requires 2 byte alignment
0x5b7a7f829033: note: pointer points here
 ff  ff ff ff 00 44 00 43 01  34 58 54 01 01 06 00 85  95 80 60 00 00 00 00 00  00 00 00 00 00 00 00
              ^
    #0 0x5b7a71a5887e in net_checksum_calculate /home/pm215/qemu/build/clang/../../net/checksum.c:168:24
    #1 0x5b7a7156819a in gem_transmit /home/pm215/qemu/build/clang/../../hw/net/cadence_gem.c:1386:21
    #2 0x5b7a71566201 in gem_write /home/pm215/qemu/build/clang/../../hw/net/cadence_gem.c:1650:13

Fix this by marking the udp_header struct as QEMU_PACKED,
so that the compiler knows it might be unaligned and will
generate the right code for accessing fields.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>
Message-ID: <20260212140917.1443253-5-peter.maydell@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
---
 include/net/eth.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/net/eth.h b/include/net/eth.h
index 63f598d7cdd..df90ff08374 100644
--- a/include/net/eth.h
+++ b/include/net/eth.h
@@ -85,7 +85,7 @@ typedef struct udp_header {
     uint16_t uh_dport; /* destination port */
     uint16_t uh_ulen;  /* udp length */
     uint16_t uh_sum;   /* udp checksum */
-} udp_header;
+} QEMU_PACKED udp_header;
 
 typedef struct ip_pseudo_header {
     uint32_t ip_src;
-- 
2.52.0