# CVE-2025-38723: LoongArch: BPF: Fix jump offset calculation in tailcall

CVE-2025-38723 is fixed in linux on 1 platform, first by DEBIAN-CVE-2025-38723, released September 4, 2025. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2025-38723
- Priority: Routine
- CVSS: 5.5 (medium)
- EPSS: 0.0017
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Sep 4, 2025
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-38723

## Description

In the Linux kernel, the following vulnerability has been resolved:  LoongArch: BPF: Fix jump offset calculation in tailcall  The extra pass of bpf_int_jit_compile() skips JIT context initialization which essentially skips offset calculation leaving out_offset = -1, so the jmp_offset in emit_bpf_tail_call is calculated by  "#define jmp_offset (out_offset - (cur_offset))"  is a negative number, which is wrong. The final generated assembly are as follow.  54:	bgeu        	$a2, $t1, -8	    # 0x0000004c 58:	addi.d      	$a6, $s5, -1 5c:	bltz        	$a6, -16	    # 0x0000004c 60:	alsl.d      	$t2, $a2, $a1, 0x3 64:	ld.d        	$t2, $t2, 264 68:	beq         	$t2, $zero, -28	    # 0x0000004c  Before apply this patch, the follow test case will reveal soft lock issues.  cd tools/testing/selftests/bpf/ ./test_progs --allow=tailcalls/tailcall_bpf2bpf_1  dmesg: watchdog: BUG: soft lockup - CPU#2 stuck for 26s! [test_progs:25056]

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 12.15 (bookworm) | 6.1.153-1 | [DEBIAN-CVE-2025-38723](https://patchblox.com/security/data/fix/linux/debian-cve-2025-38723.md) | Sep 4, 2025 |
| Linux | linux Debian 13.5 (trixie) | 6.12.43-1 | [DEBIAN-CVE-2025-38723](https://patchblox.com/security/data/fix/linux/debian-cve-2025-38723.md) | Sep 4, 2025 |
| Linux | linux Debian 14 | 6.16.3-1 | [DEBIAN-CVE-2025-38723](https://patchblox.com/security/data/fix/linux/debian-cve-2025-38723.md) | Sep 4, 2025 |

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