# CVE-2023-52761: linux: In the Linux kernel, the following vulnerability has been resolved:  riscv: VMAP_STACK overflow detection thread-safe...

CVE-2023-52761 is fixed in linux on 1 platform, first by DEBIAN-CVE-2023-52761, released May 21, 2024. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2023-52761
- Priority: Routine
- CVSS: 5.5 (medium)
- EPSS: 0.0027
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: May 21, 2024

## Description

In the Linux kernel, the following vulnerability has been resolved:  riscv: VMAP_STACK overflow detection thread-safe  commit 31da94c25aea ("riscv: add VMAP_STACK overflow detection") added support for CONFIG_VMAP_STACK. If overflow is detected, CPU switches to `shadow_stack` temporarily before switching finally to per-cpu `overflow_stack`.  If two CPUs/harts are racing and end up in over flowing kernel stack, one or both will end up corrupting each other state because `shadow_stack` is not per-cpu. This patch optimizes per-cpu overflow stack switch by directly picking per-cpu `overflow_stack` and gets rid of `shadow_stack`.  Following are the changes in this patch   - Defines an asm macro to obtain per-cpu symbols in destination    register.  - In entry.S, when overflow is detected, per-cpu overflow stack is    located using per-cpu asm macro. Computing per-cpu symbol requires    a temporary register. x31 is saved away into CSR_SCRATCH    (CSR_SCRATCH is anyways zero since we're in kernel).  Please see Links for additional relevant disccussion and alternative solution.  Tested by `echo EXHAUST_STACK > /sys/kernel/debug/provoke-crash/DIRECT` Kernel crash log below   Insufficient stack space to handle exception!/debug/provoke-crash/DIRECT  Task stack:     [0xff20000010a98000..0xff20000010a9c000]  Overflow stack: [0xff600001f7d98370..0xff600001f7d99370]  CPU: 1 PID: 205 Comm: bash Not tainted 6.1.0-rc2-00001-g328a1f96f7b9 #34  Hardware name: riscv-virtio,qemu (DT)  epc : __memset+0x60/0xfc   ra : recursive_loop+0x48/0xc6 [lkdtm]  epc : ffffffff808de0e4 ra : ffffffff0163a752 sp : ff20000010a97e80   gp : ffffffff815c0330 tp : ff600000820ea280 t0 : ff20000010a97e88   t1 : 000000000000002e t2 : 3233206874706564 s0 : ff20000010a982b0   s1 : 0000000000000012 a0 : ff20000010a97e88 a1 : 0000000000000000   a2 : 0000000000000400 a3 : ff20000010a98288 a4 : 0000000000000000   a5 : 0000000000000000 a6 : fffffffffffe43f0 a7 : 00007fffffffffff   s2 : ff20000010a97e88 s3 : ffffffff01644680 s4 : ff20000010a9be90   s5 : ff600000842ba6c0 s6 : 00aaaaaac29e42b0 s7 : 00fffffff0aa3684   s8 : 00aaaaaac2978040 s9 : 0000000000000065 s10: 00ffffff8a7cad10   s11: 00ffffff8a76a4e0 t3 : ffffffff815dbaf4 t4 : ffffffff815dbaf4   t5 : ffffffff815dbab8 t6 : ff20000010a9bb48  status: 0000000200000120 badaddr: ff20000010a97e88 cause: 000000000000000f  Kernel panic - not syncing: Kernel stack overflow  CPU: 1 PID: 205 Comm: bash Not tainted 6.1.0-rc2-00001-g328a1f96f7b9 #34  Hardware name: riscv-virtio,qemu (DT)  Call Trace:  [<ffffffff80006754>] dump_backtrace+0x30/0x38  [<ffffffff808de798>] show_stack+0x40/0x4c  [<ffffffff808ea2a8>] dump_stack_lvl+0x44/0x5c  [<ffffffff808ea2d8>] dump_stack+0x18/0x20  [<ffffffff808dec06>] panic+0x126/0x2fe  [<ffffffff800065ea>] walk_stackframe+0x0/0xf0  [<ffffffff0163a752>] recursive_loop+0x48/0xc6 [lkdtm]  SMP: stopping secondary CPUs  ---[ end Kernel panic - not syncing: Kernel stack overflow ]---

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 13.5 (trixie) | 6.5.13-1 | [DEBIAN-CVE-2023-52761](https://patchblox.com/security/data/fix/linux/debian-cve-2023-52761.md) | May 21, 2024 |
| Linux | linux Debian 14 | 6.5.13-1 | [DEBIAN-CVE-2023-52761](https://patchblox.com/security/data/fix/linux/debian-cve-2023-52761.md) | May 21, 2024 |

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