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. > > Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx> > > --- > > arch/x86/platform/efi/efi_64.c | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c > > index c13fa2150976..6ec58ff60b56 100644 > > --- a/arch/x86/platform/efi/efi_64.c > > +++ b/arch/x86/platform/efi/efi_64.c > > @@ -391,11 +391,11 @@ int __init efi_setup_page_tables(unsigned long pa_memmap, unsigned num_pages) > > > > efi_scratch.phys_stack = page_to_phys(page + 1); /* stack grows down */ > > > > - npages = (_etext - _text) >> PAGE_SHIFT; > > + npages = (__end_rodata_aligned - _text) >> PAGE_SHIFT; > > text = __pa(_text); > > pfn = text >> PAGE_SHIFT; > > > > - pf = _PAGE_RW | _PAGE_ENC; > > + pf = _PAGE_ENC; > > if (kernel_map_pages_in_pgd(pgd, pfn, text, npages, pf)) { > > pr_err("Failed to map kernel text 1:1\n"); > > return 1; > > > > thanks, > -- > js > suse labs
