linux-kernel - Re: kexec reboot failed due to commit 75d090fd167ac

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Message-ID: <20230911155340.mzfngcnjpazwsn76@box.shutemov.name>
Date:   Mon, 11 Sep 2023 18:53:40 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     Dave Young <dyoung@...hat.com>, Ard Biesheuvel <ardb@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Aaron Lu <aaron.lu@...el.com>,
        Bagas Sanjaya <bagasdotme@...il.com>,
        Borislav Petkov <bp@...en8.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Regressions <regressions@...ts.linux.dev>,
        kexec@...ts.infradead.org
Subject: Re: kexec reboot failed due to commit 75d090fd167ac

On Mon, Sep 11, 2023 at 10:33:01AM -0500, Tom Lendacky wrote:
> On 9/11/23 09:57, Kirill A. Shutemov wrote:
> > On Mon, Sep 11, 2023 at 10:56:36PM +0800, Dave Young wrote:
> > > > early console in extract_kernel
> > > > input_data: 0x000000807eb433a8
> > > > input_len: 0x0000000000d26271
> > > > output: 0x000000807b000000
> > > > output_len: 0x0000000004800c10
> > > > kernel_total_size: 0x0000000003e28000
> > > > needed_size: 0x0000000004a00000
> > > > trampoline_32bit: 0x000000000009d000
> > > > 
> > > > Decompressing Linux... out of pgt_buf in arch/x86/boot/compressed/ident_map_64.c!?
> > > > pages->pgt_buf_offset: 0x0000000000006000
> > > > pages->pgt_buf_size: 0x0000000000006000
> > > > 
> > > > 
> > > > Error: kernel_ident_mapping_init() failed
> > > > 
> > > > It crashes on #PF due to stbl->nr_tables dereference in
> > > > efi_get_conf_table() called from init_unaccepted_memory().
> > > > 
> > > > I don't see anything special about stbl location: 0x775d6018.
> > > > 
> > > > One other bit of information: disabling 5-level paging also helps the
> > > > issue.
> > > > 
> > > > I will debug further.
> > 
> > The problem is not limited to unaccepted memory, it also triggers if we
> > reach efi_get_rsdp_addr() in the same setup.
> > 
> > I think we have several problems here.
> > 
> > - 6 pages for !RANDOMIZE_BASE is only enough for kernel, cmdline,
> >    boot_data and setup_data if we assume that they are in different 1G
> >    regions and do not cross the 1G boundaries. 4-level paging: 1 for PGD, 1
> >    for PUD, 4 for PMD tables.
> > 
> >    Looks like we never map EFI/ACPI memory explicitly.
> > 
> >    It might work if kernel/cmdline/... are in single 1G and we have
> >    spare pages to handle page faults.
> > 
> > - No spare memory to handle mapping for cc_info and cc_info->cpuid_phys;
> > 
> > - I didn't increase BOOT_INIT_PGT_SIZE when added 5-level paging support.
> >    And if start pagetables from scratch ('else' case of 'if (p4d_offset...))
> >    we run out of memory.
> > 
> > I believe similar logic would apply for BOOT_PGT_SIZE for RANDOMIZE_BASE=y
> > case.
> > 
> > I don't know what the right fix here. We can increase the constants to be
> > enough to cover existing cases, but it is very fragile. I am not sure I
> > saw all users. Some of them could silently handled with pagefault handler
> > in some setups. And it is hard to catch new users during code review.
> > 
> > Also I'm not sure why do we need pagefault handler there. Looks like it
> > just masking problems. I think everything has to be mapped explicitly.
> > 
> > Any comments?
> 
> There was a similar related issue around the cc_info blob that is captured
> here: https://lore.kernel.org/lkml/20230601072043.24439-1-ltao@redhat.com/
> 
> Personally, I'm a fan of mapping the EFI tables that will be passed to the
> kexec/kdump kernel. To me, that seems to more closely match the valid
> mappings for the tables when control is transferred to the OS from UEFI on
> the initial boot.

I don't see how it would help if initialize_identity_maps() resets
pagetables. See 'else' case of 'if (p4d_offset...).

-- 
  Kiryl Shutsemau / Kirill A. Shutemov