# CVE-2021-47414: linux: In the Linux kernel, the following vulnerability has been resolved:  riscv: Flush current cpu icache before other cpu...

CVE-2021-47414 is fixed in linux on 1 platform, first by DEBIAN-CVE-2021-47414, released May 21, 2024. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2021-47414
- Priority: Routine
- CVSS: 5.5 (medium)
- EPSS: 0.0022
- 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: Flush current cpu icache before other cpus  On SiFive Unmatched, I recently fell onto the following BUG when booting:  [    0.000000] ftrace: allocating 36610 entries in 144 pages [    0.000000] Oops - illegal instruction [#1] [    0.000000] Modules linked in: [    0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 5.13.1+ #5 [    0.000000] Hardware name: SiFive HiFive Unmatched A00 (DT) [    0.000000] epc : riscv_cpuid_to_hartid_mask+0x6/0xae [    0.000000]  ra : __sbi_rfence_v02+0xc8/0x10a [    0.000000] epc : ffffffff80007240 ra : ffffffff80009964 sp : ffffffff81803e10 [    0.000000]  gp : ffffffff81a1ea70 tp : ffffffff8180f500 t0 : ffffffe07fe30000 [    0.000000]  t1 : 0000000000000004 t2 : 0000000000000000 s0 : ffffffff81803e60 [    0.000000]  s1 : 0000000000000000 a0 : ffffffff81a22238 a1 : ffffffff81803e10 [    0.000000]  a2 : 0000000000000000 a3 : 0000000000000000 a4 : 0000000000000000 [    0.000000]  a5 : 0000000000000000 a6 : ffffffff8000989c a7 : 0000000052464e43 [    0.000000]  s2 : ffffffff81a220c8 s3 : 0000000000000000 s4 : 0000000000000000 [    0.000000]  s5 : 0000000000000000 s6 : 0000000200000100 s7 : 0000000000000001 [    0.000000]  s8 : ffffffe07fe04040 s9 : ffffffff81a22c80 s10: 0000000000001000 [    0.000000]  s11: 0000000000000004 t3 : 0000000000000001 t4 : 0000000000000008 [    0.000000]  t5 : ffffffcf04000808 t6 : ffffffe3ffddf188 [    0.000000] status: 0000000200000100 badaddr: 0000000000000000 cause: 0000000000000002 [    0.000000] [<ffffffff80007240>] riscv_cpuid_to_hartid_mask+0x6/0xae [    0.000000] [<ffffffff80009474>] sbi_remote_fence_i+0x1e/0x26 [    0.000000] [<ffffffff8000b8f4>] flush_icache_all+0x12/0x1a [    0.000000] [<ffffffff8000666c>] patch_text_nosync+0x26/0x32 [    0.000000] [<ffffffff8000884e>] ftrace_init_nop+0x52/0x8c [    0.000000] [<ffffffff800f051e>] ftrace_process_locs.isra.0+0x29c/0x360 [    0.000000] [<ffffffff80a0e3c6>] ftrace_init+0x80/0x130 [    0.000000] [<ffffffff80a00f8c>] start_kernel+0x5c4/0x8f6 [    0.000000] ---[ end trace f67eb9af4d8d492b ]--- [    0.000000] Kernel panic - not syncing: Attempted to kill the idle task! [    0.000000] ---[ end Kernel panic - not syncing: Attempted to kill the idle task! ]---  While ftrace is looping over a list of addresses to patch, it always failed when patching the same function: riscv_cpuid_to_hartid_mask. Looking at the backtrace, the illegal instruction is encountered in this same function. However, patch_text_nosync, after patching the instructions, calls flush_icache_range. But looking at what happens in this function:  flush_icache_range -> flush_icache_all                    -> sbi_remote_fence_i                    -> __sbi_rfence_v02                    -> riscv_cpuid_to_hartid_mask  The icache and dcache of the current cpu are never synchronized between the patching of riscv_cpuid_to_hartid_mask and calling this same function.  So fix this by flushing the current cpu's icache before asking for the other cpus to do the same.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 12.15 (bookworm) | 5.14.12-1 | [DEBIAN-CVE-2021-47414](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47414.md) | May 21, 2024 |
| Linux | linux Debian 13.5 (trixie) | 5.14.12-1 | [DEBIAN-CVE-2021-47414](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47414.md) | May 21, 2024 |
| Linux | linux Debian 14 | 5.14.12-1 | [DEBIAN-CVE-2021-47414](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47414.md) | May 21, 2024 |

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