Description

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

arm64: Restrict CPU_BIG_ENDIAN to GNU as or LLVM IAS 15.x or newer

Prior to LLVM 15.0.0, LLVM's integrated assembler would incorrectly
byte-swap NOP when compiling for big-endian, and the resulting series of
bytes happened to match the encoding of FNMADD S21, S30, S0, S0.

This went unnoticed until commit:

34f66c4c4d5518c1 ("arm64: Use a positive cpucap for FP/SIMD")

Prior to that commit, the kernel would always enable the use of FPSIMD
early in boot when __cpu_setup() initialized CPACR_EL1, and so usage of
FNMADD within the kernel was not detected, but could result in the
corruption of user or kernel FPSIMD state.

After that commit, the instructions happen to trap during boot prior to
FPSIMD being detected and enabled, e.g.

| Unhandled 64-bit el1h sync exception on CPU0, ESR 0x000000001fe00000 -- ASIMD
| CPU: 0 PID: 0 Comm: swapper Not tainted 6.6.0-rc3-00013-g34f66c4c4d55 #1
| Hardware name: linux,dummy-virt (DT)
| pstate: 400000c9 (nZcv daIF -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
| pc : __pi_strcmp+0x1c/0x150
| lr : populate_properties+0xe4/0x254
| sp : ffffd014173d3ad0
| x29: ffffd014173d3af0 x28: fffffbfffddffcb8 x27: 0000000000000000
| x26: 0000000000000058 x25: fffffbfffddfe054 x24: 0000000000000008
| x23: fffffbfffddfe000 x22: fffffbfffddfe000 x21: fffffbfffddfe044
| x20: ffffd014173d3b70 x19: 0000000000000001 x18: 0000000000000005
| x17: 0000000000000010 x16: 0000000000000000 x15: 00000000413...

Classification

CVE ID: CVE-2023-52750

Affected Products

Vendor: Linux

Product: Linux

Exploit Prediction Scoring System (EPSS)

EPSS Score: 0.04% (probability of being exploited)

EPSS Percentile: 12.41% (scored less or equal to compared to others)

EPSS Date: 2025-02-04 (when was this score calculated)

References

https://git.kernel.org/stable/c/d08a1e75253b4e19ae290b1c35349f12cfcebc0a
https://git.kernel.org/stable/c/936c9c10efaefaf1ab3ef020e1f8aaaaff1ad2f9
https://git.kernel.org/stable/c/ef0224ee5399ea8a46bc07dc6c6494961ed5fdd2
https://git.kernel.org/stable/c/bd31e534721ab95ef237020fe6995c899ffdf21a
https://git.kernel.org/stable/c/69e619d2fd056fe1f5d0adf01584f2da669e0d28
https://git.kernel.org/stable/c/146a15b873353f8ac28dc281c139ff611a3c4848

Timeline