Re:Exploiting System Management Mode with a very long interrupt
by userbinator on Monday August 10, 2026 @10:03PM
(#49252481)
SMM was originally conceived for power management, as it first appeared in the laptop-oriented 386SL. Then it was used for seamless backwards compatibility e.g. peripheral emulation. Unlike e.g. TPMs or other DRM-ish schemes, IMHO SMM was never hostile from the beginning.
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Re:Exploiting System Management Mode with a very long interrupt
by octoberfranklin on Monday August 10, 2026 @11:08PM
(#49252914)
I disagree. If it were not user hostile the days before BIOSes were cryptographically signed the SMM code would have no reason to disallow the kernel modifying or replacing it. Like `insmod` lets root-in-userspace modify kernel-privilege-level code.
In fact the whole situation is very much analogous to Kernel Lockdown, which is controversial.
With signed bootcode you can give a reason for not letting the userspace modify the SMM code. But when all this stuff was designed there were no bootcode signatures.
Re:Exploiting System Management Mode with a very long interrupt
by userbinator on Tuesday August 11, 2026 @01:50AM
(#49253834)
the SMM code would have no reason to disallow the kernel modifying or replacing it
Don't forget that SMM code started out in A0000 --- the area of RAM that would've otherwise been inaccessible and wasted anyway, because it was usually decoded to the VGA. Also, this was the era of DOS; there was no difference between "kernel" and "application".