// For flags

CVE-2021-47414

riscv: Flush current cpu icache before other cpus

Severity Score

"-"
*CVSS v-

Exploit Likelihood

*EPSS

Affected Versions

*CPE

Public Exploits

0
*Multiple Sources

Exploited in Wild

-
*KEV

Decision

Track
*SSVC
Descriptions

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.

En el kernel de Linux, se resolvió la siguiente vulnerabilidad: riscv: vaciar el icache de la CPU actual antes que otras CPU. En SiFive Unmatched, recientemente encontré el siguiente BUGal arrancar: [0.000000] ftrace: asignar 36610 entradas en 144 páginas [0.000000] Ups - instrucción ilegal [#1] [ 0.000000] Módulos vinculados en: [ 0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 5.13.1+ #5 [ 0.000000] Nombre del hardware: 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 : 00000000000000004 t2 : 00000000000000000 s0: ffffffff81803e60 [0.000000] s1: 0000000000000000 a0: ffffffff81a22238 a1: ffffffff81803e10 [0.000000] a2: 000000000000000 a3: 0000000 000000000 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: ffcf04000808 t6: ffffffe3ffddf188 [0.000000] estado : 0000000200000100 badaddr: 0000000000000000 causa: 0000000000000002 [ 0.000000] [] riscv_cpuid_to_hartid_mask+0x6/0xae [ 0.000000] ffffffff80009474&gt;] sbi_remote_fence_i+0x1e/0x26 [ 0.000000] [] Flush_icache_all+0x12/0x1a [ 0.000000] [] patch_text_nosync+0x26/0x32 [ 0.000000] [] ftrace_init_nop+0x52/0x8c [ 0.000000] [] ftrace_process_locs.isra.0+0x29c/ 0x360 [ 0.000000] [] ftrace_init+ 0x80/0x130 [ 0.000000] [] start_kernel+0x5c4/0x8f6 [ 0.000000] ---[ end trace f67eb9af4d8d492b ]--- [ 0.000000] Pánico en el kernel - no se sincroniza: ¡Intentó finalizar la tarea inactiva! [0.000000] ---[ fin del pánico del kernel: no se sincroniza: ¡se intentó finalizar la tarea inactiva! ]--- Mientras ftrace recorre una lista de direcciones para parchear, siempre fallaba al parchear la misma función: riscv_cpuid_to_hartid_mask. Al observar el seguimiento, la instrucción ilegal se encuentra en esta misma función. Sin embargo, patch_text_nosync, después de parchear las instrucciones, llama a flush_icache_range. Pero observando lo que sucede en esta función: Flush_icache_range -&gt; Flush_icache_all -&gt; sbi_remote_fence_i -&gt; __sbi_rfence_v02 -&gt; riscv_cpuid_to_hartid_mask El icache y el dcache de la CPU actual nunca se sincronizan entre el parche de riscv_cpuid_to_hartid_mask y la llamada a esta misma función. Así que solucione este problema limpiando el icache de la CPU actual antes de pedirle a las otras CPU que hagan lo mismo.

*Credits: N/A
CVSS Scores
Attack Vector
-
Attack Complexity
-
Privileges Required
-
User Interaction
-
Scope
-
Confidentiality
-
Integrity
-
Availability
-
* Common Vulnerability Scoring System
SSVC
  • Decision:Track
Exploitation
None
Automatable
No
Tech. Impact
Partial
* Organization's Worst-case Scenario
Timeline
  • 2024-05-21 CVE Reserved
  • 2024-05-21 CVE Published
  • 2024-05-22 EPSS Updated
  • 2024-12-19 CVE Updated
  • ---------- Exploited in Wild
  • ---------- KEV Due Date
  • ---------- First Exploit
CWE
CAPEC
Affected Vendors, Products, and Versions
Vendor Product Version Other Status
Vendor Product Version Other Status <-- --> Vendor Product Version Other Status
Linux
Search vendor "Linux"
Linux Kernel
Search vendor "Linux" for product "Linux Kernel"
>= 4.15 < 5.10.73
Search vendor "Linux" for product "Linux Kernel" and version " >= 4.15 < 5.10.73"
en
Affected
Linux
Search vendor "Linux"
Linux Kernel
Search vendor "Linux" for product "Linux Kernel"
>= 4.15 < 5.14.12
Search vendor "Linux" for product "Linux Kernel" and version " >= 4.15 < 5.14.12"
en
Affected
Linux
Search vendor "Linux"
Linux Kernel
Search vendor "Linux" for product "Linux Kernel"
>= 4.15 < 5.15
Search vendor "Linux" for product "Linux Kernel" and version " >= 4.15 < 5.15"
en
Affected