linux-cve-announce - CVE-2025-40079: riscv, bpf: Sign extend struct ops return values properly

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Message-ID: <2025102820-CVE-2025-40079-6b2a@gregkh>
Date: Tue, 28 Oct 2025 12:48:56 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-40079: riscv, bpf: Sign extend struct ops return values properly

From: Greg Kroah-Hartman <gregkh@...nel.org>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

riscv, bpf: Sign extend struct ops return values properly

The ns_bpf_qdisc selftest triggers a kernel panic:

    Unable to handle kernel paging request at virtual address ffffffffa38dbf58
    Current test_progs pgtable: 4K pagesize, 57-bit VAs, pgdp=0x00000001109cc000
    [ffffffffa38dbf58] pgd=000000011fffd801, p4d=000000011fffd401, pud=000000011fffd001, pmd=0000000000000000
    Oops [#1]
    Modules linked in: bpf_testmod(OE) xt_conntrack nls_iso8859_1 [...] [last unloaded: bpf_testmod(OE)]
    CPU: 1 UID: 0 PID: 23584 Comm: test_progs Tainted: G        W  OE       6.17.0-rc1-g2465bb83e0b4 #1 NONE
    Tainted: [W]=WARN, [O]=OOT_MODULE, [E]=UNSIGNED_MODULE
    Hardware name: Unknown Unknown Product/Unknown Product, BIOS 2024.01+dfsg-1ubuntu5.1 01/01/2024
    epc : __qdisc_run+0x82/0x6f0
     ra : __qdisc_run+0x6e/0x6f0
    epc : ffffffff80bd5c7a ra : ffffffff80bd5c66 sp : ff2000000eecb550
     gp : ffffffff82472098 tp : ff60000096895940 t0 : ffffffff8001f180
     t1 : ffffffff801e1664 t2 : 0000000000000000 s0 : ff2000000eecb5d0
     s1 : ff60000093a6a600 a0 : ffffffffa38dbee8 a1 : 0000000000000001
     a2 : ff2000000eecb510 a3 : 0000000000000001 a4 : 0000000000000000
     a5 : 0000000000000010 a6 : 0000000000000000 a7 : 0000000000735049
     s2 : ffffffffa38dbee8 s3 : 0000000000000040 s4 : ff6000008bcda000
     s5 : 0000000000000008 s6 : ff60000093a6a680 s7 : ff60000093a6a6f0
     s8 : ff60000093a6a6ac s9 : ff60000093140000 s10: 0000000000000000
     s11: ff2000000eecb9d0 t3 : 0000000000000000 t4 : 0000000000ff0000
     t5 : 0000000000000000 t6 : ff60000093a6a8b6
    status: 0000000200000120 badaddr: ffffffffa38dbf58 cause: 000000000000000d
    [<ffffffff80bd5c7a>] __qdisc_run+0x82/0x6f0
    [<ffffffff80b6fe58>] __dev_queue_xmit+0x4c0/0x1128
    [<ffffffff80b80ae0>] neigh_resolve_output+0xd0/0x170
    [<ffffffff80d2daf6>] ip6_finish_output2+0x226/0x6c8
    [<ffffffff80d31254>] ip6_finish_output+0x10c/0x2a0
    [<ffffffff80d31446>] ip6_output+0x5e/0x178
    [<ffffffff80d2e232>] ip6_xmit+0x29a/0x608
    [<ffffffff80d6f4c6>] inet6_csk_xmit+0xe6/0x140
    [<ffffffff80c985e4>] __tcp_transmit_skb+0x45c/0xaa8
    [<ffffffff80c995fe>] tcp_connect+0x9ce/0xd10
    [<ffffffff80d66524>] tcp_v6_connect+0x4ac/0x5e8
    [<ffffffff80cc19b8>] __inet_stream_connect+0xd8/0x318
    [<ffffffff80cc1c36>] inet_stream_connect+0x3e/0x68
    [<ffffffff80b42b20>] __sys_connect_file+0x50/0x88
    [<ffffffff80b42bee>] __sys_connect+0x96/0xc8
    [<ffffffff80b42c40>] __riscv_sys_connect+0x20/0x30
    [<ffffffff80e5bcae>] do_trap_ecall_u+0x256/0x378
    [<ffffffff80e69af2>] handle_exception+0x14a/0x156
    Code: 892a 0363 1205 489c 8bc1 c7e5 2d03 084a 2703 080a (2783) 0709
    ---[ end trace 0000000000000000 ]---

The bpf_fifo_dequeue prog returns a skb which is a pointer. The pointer
is treated as a 32bit value and sign extend to 64bit in epilogue. This
behavior is right for most bpf prog types but wrong for struct ops which
requires RISC-V ABI.

So let's sign extend struct ops return values according to the function
model and RISC-V ABI([0]).

  [0]: https://riscv.org/wp-content/uploads/2024/12/riscv-calling.pdf

The Linux kernel CVE team has assigned CVE-2025-40079 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 6.6 with commit 25ad10658dc1068a671553ff10e19a812c2a3783 and fixed in 6.12.53 with commit 92751937f12a7d34ad492577a251c94a55e97e72
	Issue introduced in 6.6 with commit 25ad10658dc1068a671553ff10e19a812c2a3783 and fixed in 6.17.3 with commit 918a399501e28e0cc36dbd1fcfb4208f8aa1e4d1
	Issue introduced in 6.6 with commit 25ad10658dc1068a671553ff10e19a812c2a3783 and fixed in 6.18-rc1 with commit fd2e08128944a7679e753f920e9eda72057e427c

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2025-40079
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	arch/riscv/net/bpf_jit_comp64.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/92751937f12a7d34ad492577a251c94a55e97e72
	https://git.kernel.org/stable/c/918a399501e28e0cc36dbd1fcfb4208f8aa1e4d1
	https://git.kernel.org/stable/c/fd2e08128944a7679e753f920e9eda72057e427c