SIGILL in detect_arm_hwf_by_toolchain under FreeBSD arm64 on a Raspberry Pi 4B

[Jussi Kivilinna]

Hello,

On 9.7.2024 20.49, Naram Qashat via Gcrypt-devel wrote:
> I don't know if this started to happen after I updated to FreeBSD 14.1 on my RPi4B, but libgcrypt crashes with a SIGILL in detect_arm_hwf_by_toolchain on line 527 when trying to run the assembly code there. As a result, I cannot use gnupg either. I asked about this in one of the FreeBSD IRC channels and this was the conversation about it:

Looking at documentation for __ARM_FEATURE_CRYPTO (https://github.com/ARM-software/acle/releases/download/r2024Q2/acle-2024Q2.pdf):

"__ARM_FEATURE_CRYPTO is defined to 1 if the Armv8-A Crypto instructions are supported and intrinsics targeting them are available. These instructions include AES{E, D}, SHA1{C, P, M} and others. This also implies __ARM_FEATURE_AES and __ARM_FEATURE_SHA2."

And as __ARM_FEATURE_AES is implied:

"__ARM_FEATURE_AES is defined to 1 if there is hardware support for the Advanced SIMD AES Crypto instructions from Armv8-A ..."

Based on this, libgcrypt has been compiled using CPU target that supports crypto-extensions, but actually HW does not support. Did you use "-mcpu=cortex-a72" for compiler flags to select CPU type? If compiler is enabling crypto-extensions for "-mcpu=cortex-a72" and crypto-extensions are actually optional for Cortex-A72 then bug must be in compiler... "-mcpu=cortex-a72" setting should not be selecting optional crypto-extensions by default. Which compiler are you using? GCC or clang or something else? Which version?

-Jussi

> 
> [07/09/2024 10:33:10 -4] <CBX-AWAY> So I build all my packages for my RPi4 via poudriere with CPUTYPE set to cortex-a72, and now for some reason, gpg2 crashes in libgcrypt when trying to run the asm to detect CPU features, specifically with a SIGILL: illegal trap. Specifically it crashes at this line: https://fossies.org/dox/libgcrypt-1.11.0/hwf-arm_8c_source.html#l00527
> [07/09/2024 10:35:01 -4] <@fuz> ouch
> [07/09/2024 10:35:25 -4] <@fuz> CBX-AWAY: that's a crypto instruction, they're optional on the A72 and the rpi4 doesn't have them
> [07/09/2024 10:36:37 -4] <CBX-AWAY> That is an ouch indeed. Now I wonder what I can do about it, if there is even anything I can do about it.
> [07/09/2024 10:37:33 -4] <@fuz> not sure
> [07/09/2024 10:42:05 -4] <jhibbits> Is there a compiler flag to disable crypto?
> [07/09/2024 10:42:29 -4] <@fuz> jhibbits: by default it's not enabled
> [07/09/2024 10:42:37 -4] <@fuz> you have to add +crypto to enable it
> [07/09/2024 10:42:40 -4] <jhibbits> ah
> [07/09/2024 10:43:26 -4] <jhibbits> So libgcrypt assumes that it's enabled, or tries to use a SIGILL handler to confirm?
> [07/09/2024 10:44:15 -4] <@fuz> the code linked looks like it exercises the assembler
> [07/09/2024 10:44:22 -4] <@fuz> to check if the mnemonics are supported
> [07/09/2024 10:44:54 -4] <jhibbits> That code is all sorts of wrong
> [07/09/2024 10:56:42 -4] <jhibbits> OR-ing in all options supported by the compiler, whether supported by the hardware or not, is very wrong.
> [07/09/2024 10:57:33 -4] <jhibbits> CBX-AWAY: you should file a bug with libgcrypt to fix that brokenness
> [07/09/2024 10:57:38 -4] <@fuz> jhibbits: if you build for a distribution, it makes sense to build a binary that can use all features the compiler supports, so you can select at runtime what you need.
> [07/09/2024 10:58:15 -4] <jhibbits> fuz: yes, but this is a runtime file
> [07/09/2024 10:59:33 -4] <jhibbits> fuz: it's explicitly ORing in all compiler-supported features, whether supported by the hardware (via HW_CAP or /proc/cpuinfo, or sysctl).
> [07/09/2024 10:59:42 -4] <jhibbits> It should be taking a subset of those.
> [07/09/2024 11:03:19 -4] <@fuz> ok that's weird
> [07/09/2024 11:03:26 -4] <@fuz> though on freebsd we only support HW_CAP
> [07/09/2024 11:03:35 -4] <@fuz> and reading the special registers directly
> [07/09/2024 11:03:46 -4] <@fuz> so idk what other data sources there are
> [07/09/2024 11:04:07 -4] <jhibbits> That's all that should be needed
> [07/09/2024 11:04:48 -4] <jhibbits> That detect_arm_hwf_by_toolchain() is severely broken, and shouldn't exist.
> 
> I'm not sure what the actual fix is for this, and I cannot post this to the GnuPG issue tracker as I don't have an account and registration there is disabled. If it would be better for me to post this on the issue tracker, then for my account, I'd like the handle CyberBotX, my shown name as Naram Qashat, and my email address as cyberbotx at cyberbotx.com.
> 
> Thanks in advance,
> Naram "CyberBotX" Qashat
> 
> _______________________________________________
> Gcrypt-devel mailing list
> Gcrypt-devel at gnupg.org
> https://lists.gnupg.org/mailman/listinfo/gcrypt-devel