RETBleed: WARNING: Spectre v2 mitigation leaves CPU vulnerable to RETBleed attacks, data leaks possible!

[Naresh Kamboju]

Results from Linaro’s test farm.

We are booting the i386 kernel on an x86 machine.
With Spectre V2 patches merged into Linux mainline we have been noticing
RETBleed: WARNING: Spectre v2 mitigation leaves CPU vulnerable to
RETBleed attacks, data leaks possible!
Please find the detailed boot log in the below link [1] and [2].

Reported-by: Linux Kernel Functional Testing <lkft@xxxxxxxxxx>

metadata:
  git_ref: master
  git_repo: https://gitlab.com/Linaro/lkft/mirrors/torvalds/linux-mainline
  git_sha: 4a57a8400075bc5287c5c877702c68aeae2a033d
  git_describe: v5.19-rc6-115-g4a57a8400075
  kernel_version: 5.19.0-rc6
  kernel-config: https://builds.tuxbuild.com/2Bu6unA4pJ0TotIOQ6jcNKfhmew/config
  build-url: https://gitlab.com/Linaro/lkft/mirrors/torvalds/linux-mainline/-/pipelines/587353280
  artifact-location: https://builds.tuxbuild.com/2Bu6unA4pJ0TotIOQ6jcNKfhmew
  toolchain: gcc-11

boot log:
---------
[    0.000000] Linux version 5.19.0-rc6 (tuxmake@tuxmake)
(i686-linux-gnu-gcc (Debian 11.3.0-3) 11.3.0, GNU ld (GNU Binutils for
Debian) 2.38) #1 SMP PREEMPT_DYNAMIC @1657744061
[    0.000000] x86/fpu: Supporting XSAVE feature 0x001: 'x87 floating
point registers'

<trim>

[    1.275957] LSM: Security Framework initializing
[    1.275957] SELinux:  Initializing.
[    1.275957] Mount-cache hash table entries: 2048 (order: 1, 8192
bytes, linear)
[    1.275957] Mountpoint-cache hash table entries: 2048 (order: 1,
8192 bytes, linear)
[    1.275957] CPU0: Thermal monitoring enabled (TM1)
[    1.275957] process: using mwait in idle threads
[    1.275957] Last level iTLB entries: 4KB 128, 2MB 8, 4MB 8
[    1.275957] Last level dTLB entries: 4KB 64, 2MB 0, 4MB 0, 1GB 4
[    1.275957] Spectre V1 : Mitigation: usercopy/swapgs barriers and
__user pointer sanitization
[    1.275957] Spectre V2 : Mitigation: Retpolines
[    1.275957] Spectre V2 : Spectre v2 / SpectreRSB mitigation:
Filling RSB on context switch
[    1.275957] RETBleed: WARNING: Spectre v2 mitigation leaves CPU
vulnerable to RETBleed attacks, data leaks possible!
[    1.275957] RETBleed: Vulnerable
[    1.275957] Speculative Store Bypass: Vulnerable
[    1.275957] L1TF: Kernel not compiled for PAE. No mitigation for L1TF
[    1.275957] MDS: Vulnerable: Clear CPU buffers attempted, no microcode
[    1.275957] TAA: Vulnerable: Clear CPU buffers attempted, no microcode
[    1.275957] MMIO Stale Data: Vulnerable: Clear CPU buffers
attempted, no microcode
[    1.275957] SRBDS: Vulnerable: No microcode

Full test log link,
[1] https://lkft.validation.linaro.org/scheduler/job/5282509#L490
[2] https://qa-reports.linaro.org/lkft/linux-mainline-master-sanity/build/v5.19-rc6-115-g4a57a8400075/testrun/10817056/suite/log-parser-boot/tests/

Best regards
Naresh Kamboju

--
Linaro LKFT
https://lkft.linaro.org