Messages in this thread | | | Date | Sat, 31 Dec 2022 20:33:59 -0800 | Subject | Re: [PATCH qemu] x86: don't let decompressed kernel image clobber setup_data | From | "H. Peter Anvin" <> |
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On 12/31/22 10:22, Jason A. Donenfeld wrote: > On Sat, Dec 31, 2022 at 03:24:32PM +0100, Borislav Petkov wrote: >> On Sat, Dec 31, 2022 at 02:51:28PM +0100, Jason A. Donenfeld wrote: >>> That failure is unrelated to the ident mapping issue Peter and >>> I discussed. The original failure is described in the commit message: >>> decompression clobbers the data, so sd->next points to garbage. >> >> Right > > So with that understanding confirmed, I'm confused at your surprise that > hpa's unrelated fix to the different issue didn't fix this issue. >
If decompression does clobber the data, then we *also* need to figure out why that is. There are basically three possibilities:
1. If physical KASLR is NOT used:
a. The boot loader doesn't honor the kernel safe area properly; b. Somewhere in the process a bug in the calculation of the kernel safe area has crept in.
2. If physical KASLR IS used:
The decompressor doesn't correctly keep track of nor relocate all the keep-out zones before picking a target address.
One is a bootloader bug, two is a kernel bug. My guess is (2) is the culprit, but (1b) should be checked, too.
-hpa
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