Re: [edk2] Corrupted EFI region

From: Borislav Petkov
Date: Mon Aug 05 2013 - 18:08:16 EST

On Mon, Aug 05, 2013 at 11:26:46PM +0200, Laszlo Ersek wrote:
> What happens if you pass "memblock=debug" on the kernel command line
> (see early_memblock() in "mm/memblock.c")?
> (I just tried it in my Fedora 19 guest, and it in fact produced the message
> [ 0.000000] efi: Could not reserve boot range [0x0000800000-0x0000ffffff]

Note to self: Always look for bugs in Linux' UEFI code first, before
going anywhere else!

Yes, very good analysis and good job Laszlo!

I'll write what I see now but will doublecheck it tomorrow because I'm
almost half asleep.

[ 0.000000] efi: efi_reserve_boot_services: -> start: 0x7e0ad000, size: 0x1f000
[ 0.000000] efi: Could not reserve boot range [0x007e0ad000-0x007e0cbfff]

And yes, this fails because memblock_is_region_reserved(start, size)
returns true.

And why is that:

[ 0.000000] memblock_reserve: [0x000000036be000-0x000000036c3000] setup_arch+0x60e/0xa63
[ 0.000000] MEMBLOCK configuration:
[ 0.000000] memory size = 0x7fef1000 reserved size = 0x1724570
[ 0.000000] memory.cnt = 0x4
[ 0.000000] memory[0x0] [0x00000000001000-0x0000000009ffff], 0x9f000 bytes
[ 0.000000] memory[0x1] [0x00000000100000-0x0000007e667fff], 0x7e568000 bytes
[ 0.000000] memory[0x2] [0x0000007e692000-0x0000007fb11fff], 0x1480000 bytes
[ 0.000000] memory[0x3] [0x0000007fb76000-0x0000007ffdffff], 0x46a000 bytes
[ 0.000000] reserved.cnt = 0x3
[ 0.000000] reserved[0x0] [0x0000000009f000-0x000000000fffff], 0x61000 bytes
[ 0.000000] reserved[0x1] [0x00000002000000-0x000000036c2fff], 0x16c3000 bytes
[ 0.000000] reserved[0x2] [0x0000007e0ad018-0x0000007e0ad587], 0x570 bytes

There are 0x570 bytes right in this region which are memblock-reserved
and so we truncate it in efi_reserve_boot_services().

This makes me say words which will offend this list so I'll instead go
out on the balcony and wake up the neighbors. :-)

Ok, thanks again for finding it, I'll go and try to figure out the whole
mess tomorrow.

Good night!

> BTW, regarding Michael's answer, I think this is just one of several
> ways in which Linux manipulates the EFI memmap between (b) and (c).
> For example it seems to merge ranges in the map.

Yes, it does so in efi_enter_virtual_mode(). That was my initial
suspicion, that's why I dumped the regions before the merging.



Sent from a fat crate under my desk. Formatting is fine.
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