Re: [Crash-utility] Not compatible with d52888aa2753 ("x86/mm: Move LDT remap out of KASLR region on 5-level paging")

Hello WANG, I've applied a patch upstream that addresses the issue automatically for 4.20 and later kernels, but requires a command line option for kernels that contain a backport of kernel commit d52888aa2753. As mentioned in the commit message, that requirement may be revisited in the future -- I will entertain any patches that can cleanly make the PAGE_OFFSET determination in a fail-safe manner: https://github.com/crash-utility/crash/commit/c63d678798c21a5379f132f1241... The patch is untested as I don't have any recent kernels that are not configured with CONFIG_RANDOMIZE_BASE.

Thanks, Dave ----- Original Message ----- > > > ----- Original Message ----- > > commit d52888aa2753 ("x86/mm: Move LDT remap out of KASLR region on > > 5-level paging") changed PAGE_OFFSET from 0xffff880000000000 to > > 0xffff888000000000. > > > > crash can't open such with CONFIG_RANDOMIZE_BASE=n: > > > > crash: read error: kernel virtual address: ffff888ffe605024 type: > > "tss_struct ist array" > > > > Edit defs.h: > > > > -#define PAGE_OFFSET_2_6_27 0xffff880000000000 > > +#define PAGE_OFFSET_2_6_27 0xffff888000000000 > > > > And this works for me. > > > > (d52888aa2753 has also been included in 4.14.84) > > Ah, so your kernel does not have "page_offset_base", which simplifies > things for KASLR kernels. I don't have any sample vmcores that are not > configured with CONFIG_RANDOMIZE_BASE. > > Obviously just changing PAGE_OFFSET_2_6_27 in the crash utility as above > cannot be done for backwards compatibility purposes. > > There would have to be 2 adjustments in the crash utility for the > kernel change: > > -#define __PAGE_OFFSET_BASE_L5 _AC(0xff10000000000000, UL) > -#define __PAGE_OFFSET_BASE_L4 _AC(0xffff880000000000, UL) > +#define __PAGE_OFFSET_BASE_L5 _AC(0xff11000000000000, UL) > +#define __PAGE_OFFSET_BASE_L4 _AC(0xffff888000000000, UL) > > where the crash utility uses PAGE_OFFSET_2_6_27 and PAGE_OFFSET_5LEVEL > > #define PAGE_OFFSET_2_6_27 0xffff880000000000 > and > #define PAGE_OFFSET_5LEVEL 0xff10000000000000 > > > > > (d52888aa2753 has also been included in 4.14.84) > > > > And that's a problem. We could gate the setting of > machdep->machspec->page_offset > on LINUX(4, 20, 0), but since it's been backported, there needs to be another > way > to best determine which PAGE_OFFSET value to use when KASLR is not in effect. > > Dave > > > > > > > Thanks > > WANG Chao > > > > -- > > Crash-utility mailing list > > Crash-utility(a)redhat.com > > https://www.redhat.com/mailman/listinfo/crash-utility > > > > -- > Crash-utility mailing list > Crash-utility(a)redhat.com > https://www.redhat.com/mailman/listinfo/crash-utility > -- Crash-utility mailing list Crash-utility(a)redhat.com https://www.redhat.com/mailman/listinfo/crash-utility