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What’s scary about UEFI is that it has both direct hardware access and a massive attack surface: GUI, Ethernet stack, occasionally an 802.11 stack, etc.
Many uefi systems do lots of "fun things" because they have network access. Take a look at ASUS motherboards, which has Armory Crate in UEFI. It will download and install software in your windows install. ...automatic bloatware from the bios.
I'm impressed when they have VirtualBox or qemu running in UEFI, sandboxing my real OS.
This is potentially not the best idea in the world...
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UEFI provides an interface to register code that runs in SMM, true. SMM being a requirement is a side effect of x86 history and platform design, not UEFI (which doesn't actually require SMM).
I don't think SMM requires UEFI, either, actually... I believe there have been BIOSes that initialized SMM also.
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SMM is also part of the firmware, it is set up by UEFI.
UEFI provides an interface to register code that runs in SMM, true. SMM being a requirement is a side effect of x86 history and platform design, not UEFI (which doesn't actually require SMM).
Anyone have a favorite guide/blog post/whatever for getting started with UEFI applications?
There are several pages here under the UEFI tag. There are also some application guides and a few polished bootloader documents.
Earlier quoted context omitted.
UEFI provides an interface to register code that runs in SMM, true. SMM being a requirement is a side effect of x86 history and platform design, not UEFI (which doesn't actually require SMM).
UEFI Secure Boot requires SMM (because it secures access to the key vault). Non-x86 architectures use something else, for example they could use EL3 on ARM. Either way it's a "super-supervisor mode" of sorts.
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UEFI did not replace the BIOS. You must have an onboard storage (usually a EEPROM)that loads all the UEFI. To load the UEFI, it still needs to know about devices and such, so that onboard thing albeit we no longer allowed to call BIOS, is... the BIOS. It is the 0 stage loader, or pre-loader, or pre-UEFI boot loader; just do not call it BIOS because it hurt feelings. So what is being sold is: old way is BIOS --> MBR -…
> Something has to start reach and load the UEFI written on a 'boot media' No. The UEFI stack lives entirely in flash, the same as BIOS did.