The ESP Path Limit in HP Firmware

[ximian]

When I was installing the latest Bluefin Dakota I stumbled upon a weird bug where the system is completely unbootable after the reboot. A few sessions with various chatbots led me to the conclusion that there is a known quirk in HP firmware:

"In HP’s proprietary UEFI firmware (BIOSphere): HP's FAT implementation has a known static buffer limit in its File Path Device Path parser. When systemd-boot passes this path to UEFI BS->LoadImage(), HP’s firmware encounters a buffer overrun or silent truncation, failing to return or execute the image and locking the CPU thread."

The problem is that I couldn't find reliable information about what that limit actually is. AI suggests that's 166 characters long, but that doesn't seem to add up. On the other hand, the reality is that shortening the ESP path fixes the problem. 

[Deep_World]

Hi  @ximian 
 
Welcome to the HP Support Community!

Thanks for reaching out!

I understand you've spent considerable time investigating this and have narrowed the issue down to a potential UEFI boot path limitation. I'd be glad to help gather some additional details so we can better understand the environment and determine the most appropriate next steps.

Before we proceed, kindly note that HP provides limited support for Linux operating systems. That said, we'd still like to understand your setup and guide you where possible.

Could you kindly help us with the following information?

• What BIOS version is currently installed on the system?
• Is Secure Boot enabled or disabled?
• Is the system configured for UEFI mode only, or does it have any Legacy settings enabled?
• Is Linux the only operating system installed, or is this a dual-boot configuration?
• When the issue occurs, what exactly happens after reboot? 
  • Black screen?
  • HP logo remains displayed?
  • System powers on but does not continue booting?
  • Any error messages displayed?

In the meantime, you may try the following troubleshooting steps:

1. Update the system BIOS to the latest version available from HP.
2. Restore BIOS settings to defaults and then reconfigure only the required Linux-related settings.
3. Test with a simplified EFI boot path (shorter directory names and file names).
4. Verify that the EFI System Partition is formatted as FAT32 and passes filesystem checks.
5. Disable any custom Secure Boot keys or custom boot entries and test with a clean boot configuration.(But make sure you have the backup of the keys)
6. Create a minimal EFI boot entry manually and verify whether the firmware can load it consistently.
   
   Also kindly refer to the EFI guidelines - click here 

I hope this helps. 

[ximian]

• BIOS: 01.13.00 Rev.A
• Secure Boot Disabled
• UEFI mode only
• Linux is the only system installed
• A black screen occurs between loading the systemd-boot menu and loading the system. It's a hard lock (Caps-Lock stays unresponsive; the only way to turn off/restart the system is to hold the power button)
• After the reboot cycle repeats
• BIOS is already on the most recent version
• I've tried restoring defaults

I've already explained what the issue is - the system hard locks because of a too-long path to the boot image. I just wanted to know what the actual limit is.

The confirmed, affected systems so far:

• HP EliteBook 845 G10 (BIOS: 01.13.00 Rev.A)
• HP ZBook Firefly G10 A (BIOS: 01.12.00 Rev.A)
• HP EliteBook 840 G10 (BIOS: 01.13.01 Rev.A)

So we have two AMD and one Intel-based systems so far.

I've done some more testing in the meantime and concluded that the longest bootable boot entry is 160 characters long, if I'm counting correctly:

title Bluefin
version 20260921
linux /EFI/Linux/bootc_composefs-023cf0e317ee0f30a2f8229ed4734a136a406ed38e46abc7406948c732f23071a7b13ca652775b32d540c8b7eaba8f540fb0f479f39527fd2d2ef05094d2e/vmlinuz
initrd /EFI/Linux/bootc_composefs-023cf0e317ee0f30a2f8229ed4734a136a406ed38e46abc7406948c732f23071a7b13ca652775b32d540c8b7eaba8f540fb0f479f39527fd2d2ef05094d2e/initrd
options root=LABEL=root rw composefs=023cf0e317ee0f30a2f8229ed4734a136a406ed38e46abc7406948c732f23071a7b13ca652775b32d540c8b7eaba8f540fb0f479f39527fd2d2ef05094d2e050 rd.driver.blacklist=nouveau modprobe.blacklist=nouveau nvidia-drm.modeset=1 nvidia-drm.fbdev=1 initcall_blacklist=simpledrm_platform_driver_init zswap.enabled=1 zswap.compressor=zstd zswap.max_pool_percent=20 zswap.shrinker_enabled=1 rhgb quiet rd.luks.name=ed6fea70-3078-4bf5-b4a8-fb78715d1e3e=root
sort-key bootc-bluefin-dakota-0

 At this point, the real question is if HP wants to do something with this or not. So far, no confirmed problems on other vendors' hardware.

[Deep_World]

Hi @ximian,

Thank you for taking the time to perform such detailed testing and for sharing your findings across multiple HP platforms. 

I understand that you have already isolated the behaviour to what appears to be a firmware-related limitation involving long EFI boot paths, and that your primary concern is determining the actual path length limit rather than additional operating system troubleshooting.

As this appears to involve a potential BIOS/firmware behaviour that would require further validation by HP's engineering team, we recommend reaching out to HP Phone Support. Our phone support team can review the details you've gathered, document the affected platforms, and determine the appropriate next course of action.

They'll work with you one-on-one try to get the details you require.  

1) Click on this link—    https://support.hp.com/contact

2) Add or select the product, and change/select your region.

3) Enter the serial number of your device or select Let HP detect your product option.

4) Choose "other" option from the list

5) Select continue to contact option

You should see the HP phone support number or Chat option listed.

They will guide you further.

Or, You may also visit the nearest HP authorized service center, the service team will check and assist you.

Kindly follow this link to locate the nearest HP service center:    https://support.hp.com/us-en/help/service-center

(Select the country from the dropdown menu and enter the city name or pincode)

Have a wonderful day!

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Regards,

Deep_World