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    SubjectRe: [PATCH 05/13] efi/x86: don't map the entire kernel text RW for mixed mode
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    Ccing Gary.

    On 08. 04. 20, 12:47, Ard Biesheuvel wrote:
    > On Wed, 8 Apr 2020 at 12:42, Jiri Slaby <jslaby@suse.cz> wrote:
    >>
    >> On 13. 01. 20, 18:22, Ard Biesheuvel wrote:
    >>> The mixed mode thunking routine requires a part of it to be
    >>> mapped 1:1, and for this reason, we currently map the entire
    >>> kernel .text read/write in the EFI page tables, which is bad.
    >>>
    >>> In fact, the kernel_map_pages_in_pgd() invocation that installs
    >>> this mapping is entirely redundant, since all of DRAM is already
    >>> 1:1 mapped read/write in the EFI page tables when we reach this
    >>> point, which means that .rodata is mapped read-write as well.
    >>>
    >>> So let's remap both .text and .rodata read-only in the EFI
    >>> page tables.
    >>
    >> This patch causes unhandled page faults in mixed mode:
    >>
    >>> BUG: unable to handle page fault for address: 000000001557ee88
    >>> #PF: supervisor write access in kernel mode
    >>> #PF: error_code(0x0003) - permissions violation
    >>> PGD fd52063 P4D fd52063 PUD fd53063 PMD 154000e1
    >>> Oops: 0003 [#1] SMP PTI
    >>> CPU: 1 PID: 191 Comm: systemd-escape Not tainted
    >> 5.6.2-20.gb22bc26-default #1 openSUSE Tumbleweed (unreleased)
    >>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 0.0.0
    >> 02/06/2015
    >>> RIP: 0008:0x3d2eed95
    >>> Code: 8b 45 d4 8b 4d 10 8b 40 04 89 01 89 3b 50 6a 00 8b 55 0c 6a 00
    >> 8b 45 08 0f b6 4d e4 6a 01 31 f6 e8 ee c5 fc ff 83 c4 10 eb 07 <89> 03
    >> be 05 00 00 80 a1 74 63 31 3d 83 c0 48 e8 44 d2 ff ff eb 05
    >>> RSP: 0018:000000000fd66fa0 EFLAGS: 00010002
    >>> RAX: 0000000000000001 RBX: 000000001557ee88 RCX: 000000003d1f1120
    >>> RDX: 0000000000000001 RSI: 0000000000000000 RDI: 0000000000000001
    >>> RBP: 000000000fd66fd8 R08: 000000001557ee88 R09: 0000000000000000
    >>> R10: 0000000000000055 R11: 0000000000000000 R12: 0000000015bcf000
    >>> R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
    >>> FS: 00007f36ee9dc940(0000) GS:ffff9b903d700000(0000)
    >> knlGS:0000000000000000
    >>> CS: 0008 DS: 0018 ES: 0018 CR0: 0000000080050033
    >>> CR2: 000000001557ee88 CR3: 000000000fd5e000 CR4: 00000000000006e0
    >>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
    >>> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
    >>> Call Trace:
    >>> Modules linked in: efivarfs
    >>> CR2: 000000001557ee88
    >>
    >> EFI apparently tries to write to now read-only memory.
    >>
    >> See:
    >> https://bugzilla.suse.com/show_bug.cgi?id=1168645
    >>
    >> Reverting it on the top of 5.6 fixes the issue.
    >>
    >> I am using
    >> /usr/share/qemu/ovmf-ia32-code.bin
    >> /usr/share/qemu/ovmf-ia32-vars.bin
    >> from qemu-ovmf-ia32-202002-1.1.noarch rpm.
    >>
    >
    > Do you have a git tree for Suse's OVMF fork? I did a lot of testing
    > with upstream OVMF, and never ran into this issue.

    Not really a git tree, but the sources are here:
    https://build.opensuse.org/package/show/openSUSE:Factory/ovmf

    --
    js
    suse labs

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