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

[Emanuele Rocca <emanuele.rocca@arm.com>]

Hi,
longterm kernel 6.1.123 crashes early when booting on the Lenovo Thinkpad X13s
with the following error:

 Unable to handle kernel NULL pointer dereference at virtual address 0000000000000264

 pc: arm_smccc_version_init+0x90/0x1ac

According to faddr2line, that is line 31 of smccc.c:

 arm_smccc_version_init+0x90/0x1ac:
 arm_smccc_version_init at debian/build/build_arm64_none_arm64/drivers/firmware/smccc/smccc.c:31

 22 void __init arm_smccc_version_init(u32 version, enum arm_smccc_conduit conduit)
 23 {
 24         struct arm_smccc_res res;
 25 
 26         smccc_version = version;
 27         smccc_conduit = conduit;
 28 
 29         smccc_trng_available = smccc_probe_trng();
 30 
 31         if ((smccc_version >= ARM_SMCCC_VERSION_1_2) &&

This is with kernel 6.1.123. The last known good kernel I have available right
now is 6.1.119. In the 6.1.120 changelog I see the following commit which seems
potentially related?

 https://lore.kernel.org/all/20241106160448.2712997-1-mark.rutland@arm.com/

That's stable commit [1].

The relevant upstream commit [2] is in linux 6.12, and that kernel version does
not crash. Comparing [1] vs [2] I see differences, but I can't tell if they can
help debug the issue further. 

Thanks,
  ema

[1] https://git.kernel.org/linus/bfcaffd4cc2d61ecb0571c5baf127c4089978ad4
[2] https://git.kernel.org/linus/8c462d56487e3abdbf8a61cedfe7c795a54f4a78