[BUG] ARM64 regression: NULL pointer dereference in arm_smccc_version_init+0x90/0x1ac

[Emanuele Rocca]

Hello Will,

On 2025-02-04 10:00, Will Deacon wrote:
> Emanuele -- could you hack the code to poison the other unused result
> registers () and see if they are also cleared? ARM_SMCCC_TRNG_VERSION
> looks like a 32-bit call, so that would be W1-W7 afaict.

Not sure if this is exactly what you are asking for, but right before
the call to smccc_probe_trng():
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/drivers/firmware/smccc/smccc.c?h=v6.1.124#n29

I did the following to write to all registers. First I tried W1-W7, then
I went for W1-W17 too:

register unsigned long w1 asm("w1");
[...]
register unsigned long w17 asm("w17");

asm volatile(
  "mov w1, #0x1234\n"
  "mov w2, #0x2234\n"
  [...]
  "mov w16, #0x0234\n"
  "mov w17, #0x1234\n"
);

The values I wrote were not overwritten, see https://people.debian.org/~ema/w1-w17.jpg