Lucene search

K
cve416baaa9-dc9f-4396-8d5f-8c081fb06d67CVE-2024-35873
HistoryMay 19, 2024 - 9:15 a.m.

CVE-2024-35873

2024-05-1909:15:08
416baaa9-dc9f-4396-8d5f-8c081fb06d67
web.nvd.nist.gov
26
linux kernel
risc-v
vector state vulnerability
rt_sigreturn()
sigcontext
system call
userland application
signal handler
vstate.

6.5 Medium

AI Score

Confidence

Low

0.0004 Low

EPSS

Percentile

9.0%

In the Linux kernel, the following vulnerability has been resolved:

riscv: Fix vector state restore in rt_sigreturn()

The RISC-V Vector specification states in “Appendix D: Calling
Convention for Vector State” [1] that “Executing a system call causes
all caller-saved vector registers (v0-v31, vl, vtype) and vstart to
become unspecified.”. In the RISC-V kernel this is called “discarding
the vstate”.

Returning from a signal handler via the rt_sigreturn() syscall, vector
discard is also performed. However, this is not an issue since the
vector state should be restored from the sigcontext, and therefore not
care about the vector discard.

The “live state” is the actual vector register in the running context,
and the “vstate” is the vector state of the task. A dirty live state,
means that the vstate and live state are not in synch.

When vectorized user_from_copy() was introduced, an bug sneaked in at
the restoration code, related to the discard of the live state.

An example when this go wrong:

  1. A userland application is executing vector code
  2. The application receives a signal, and the signal handler is
    entered.
  3. The application returns from the signal handler, using the
    rt_sigreturn() syscall.
  4. The live vector state is discarded upon entering the
    rt_sigreturn(), and the live state is marked as “dirty”, indicating
    that the live state need to be synchronized with the current
    vstate.
  5. rt_sigreturn() restores the vstate, except the Vector registers,
    from the sigcontext
  6. rt_sigreturn() restores the Vector registers, from the sigcontext,
    and now the vectorized user_from_copy() is used. The dirty live
    state from the discard is saved to the vstate, making the vstate
    corrupt.
  7. rt_sigreturn() returns to the application, which crashes due to
    corrupted vstate.

Note that the vectorized user_from_copy() is invoked depending on the
value of CONFIG_RISCV_ISA_V_UCOPY_THRESHOLD. Default is 768, which
means that vlen has to be larger than 128b for this bug to trigger.

The fix is simply to mark the live state as non-dirty/clean prior
performing the vstate restore.

Affected configurations

Vulners
Node
linuxlinux_kernelRange6.86.8.5
OR
linuxlinux_kernelRange6.9.0

CNA Affected

[
  {
    "product": "Linux",
    "vendor": "Linux",
    "defaultStatus": "unaffected",
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "programFiles": [
      "arch/riscv/kernel/signal.c"
    ],
    "versions": [
      {
        "version": "c2a658d41924",
        "lessThan": "5b16d904e910",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "c2a658d41924",
        "lessThan": "c27fa53b858b",
        "status": "affected",
        "versionType": "git"
      }
    ]
  },
  {
    "product": "Linux",
    "vendor": "Linux",
    "defaultStatus": "affected",
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "programFiles": [
      "arch/riscv/kernel/signal.c"
    ],
    "versions": [
      {
        "version": "6.8",
        "status": "affected"
      },
      {
        "version": "0",
        "lessThan": "6.8",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "6.8.5",
        "lessThanOrEqual": "6.8.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "6.9",
        "lessThanOrEqual": "*",
        "status": "unaffected",
        "versionType": "original_commit_for_fix"
      }
    ]
  }
]

6.5 Medium

AI Score

Confidence

Low

0.0004 Low

EPSS

Percentile

9.0%