Linus Torvalds wrote:
On Sun, 4 Nov 2007, H. Peter Anvin wrote:
H. Peter Anvin (2):
x86 setup: add a near jump to serialize %cr0 on 386/486
x86 setup: set %ebx == %ebp == %edi == 0 on protected mode entry
Ok, I'm obviously happier, but I have to admit that the original code was
safer than the new code. It did both the short jump and the far jump
before reloading any segments.
So I suspect the new code _works_ fine, but it's simply not as
fundamentally safe as the old code was.
The old code did do some instructions in between the short jump and the
far jump, but they were all the kind of instructions that didn't care
about the PE bit: there was a _read_ of the segment descriptor value, but
that's mode-independent (it's only the writes that matter), and the other
instructions were bog-standard integer instructions.
So I would actually prefer some additional safety, with something like
the appended..
This is TOTALLY UNTESTED! I checked with objdump that the result looks
roughly ok, but I didn't really think through the segment base address in
that long jump thing. Do we have the difference between flat mode and the
16-bit bootup mode in some better way?
Hmm?
Well, we *could* do a 16-bit PM segment (and do two far jumps), but that
seems rather silly. We'd have to patch the GDT for the base in that
case, anyway.
This is more or less the same code I had for the first version of the
patch, modulo moving the short jump of course. I do like making the
32-bit code a separate function, but it really should be "movl %ecx,..."
in the 32-bit code.
I have to admit I agree with Eric that this is probably overkill, but
hey, there is nothing like a bit of overkill to make sure something is
really and truly dead.
Cooking up a tree now.
-hpa
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
