Exploiting System Management Mode with a very long interrupt

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.

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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".

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Re:Exploiting System Management Mode with a very long interrupt by inigyou on Tuesday August 11, 2026 @08:13AM (#49257026)

It's like that for reliability and compatibility. The kernel on a 386 wants to stomp over everything, so if we want the kernel to not stomp on something we'd better hide it.

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