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

[Gary Lin]

On Thu, Apr 09, 2020 at 09:51:20AM +0200, Ard Biesheuvel wrote:
> On Wed, 8 Apr 2020 at 12:51, Jiri Slaby <jslaby@xxxxxxx> wrote:
> >
> > Ccing Gary.
> >
> > On 08. 04. 20, 12:47, Ard Biesheuvel wrote:
> > > On Wed, 8 Apr 2020 at 12:42, Jiri Slaby <jslaby@xxxxxxx> 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
> >
> 
> 
> Anywhere I can get an actual build? The src rpm only has the sources,
> and the i586 rpm has nothing except
> 
> $ rpm -qlp ~/Downloads/ovmf-202002-1.1.i586.rpm
> warning: /home/ardbie01/Downloads/ovmf-202002-1.1.i586.rpm: Header V3
> RSA/SHA256 Signature, key ID 3dbdc284: NOKEY
> /usr/share/doc/packages/ovmf
> /usr/share/doc/packages/ovmf/README

Hmmm, it's weird that OBS doesn't list all derived files.
Anyway, the ia32 ovmf is available in
http://download.opensuse.org/tumbleweed/repo/oss/noarch/qemu-ovmf-ia32-202002-1.1.noarch.rpm

Gary Lin