From: Ard Biesheuvel ardb@kernel.org
commit f6103162008dfd37567f240b50e5e1ea7cf2e00c upstream.
Commit
d9e3d2c4f10320 ("efi/x86: Don't map the entire kernel text RW for mixed mode")
updated the code that creates the 1:1 memory mapping to use read-only attributes for the 1:1 alias of the kernel's text and rodata sections, to protect it from inadvertent modification. However, it failed to take into account that the unused gap between text and rodata is given to the page allocator for general use.
If the vmap'ed stack happens to be allocated from this region, any by-ref output arguments passed to EFI runtime services that are allocated on the stack (such as the 'datasize' argument taken by GetVariable() when invoked from efivar_entry_size()) will be referenced via a read-only mapping, resulting in a page fault if the EFI code tries to write to it:
BUG: unable to handle page fault for address: 00000000386aae88 #PF: supervisor write access in kernel mode #PF: error_code(0x0003) - permissions violation PGD fd61063 P4D fd61063 PUD fd62063 PMD 386000e1 Oops: 0003 [#1] SMP PTI CPU: 2 PID: 255 Comm: systemd-sysv-ge Not tainted 5.6.0-rc4-default+ #22 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 RIP: 0008:0x3eaeed95 Code: ... <89> 03 be 05 00 00 80 a1 74 63 b1 3e 83 c0 48 e8 44 d2 ff ff eb 05 RSP: 0018:000000000fd73fa0 EFLAGS: 00010002 RAX: 0000000000000001 RBX: 00000000386aae88 RCX: 000000003e9f1120 RDX: 0000000000000001 RSI: 0000000000000000 RDI: 0000000000000001 RBP: 000000000fd73fd8 R08: 00000000386aae88 R09: 0000000000000000 R10: 0000000000000002 R11: 0000000000000000 R12: 0000000000000000 R13: ffffc0f040220000 R14: 0000000000000000 R15: 0000000000000000 FS: 00007f21160ac940(0000) GS:ffff9cf23d500000(0000) knlGS:0000000000000000 CS: 0008 DS: 0018 ES: 0018 CR0: 0000000080050033 CR2: 00000000386aae88 CR3: 000000000fd6c004 CR4: 00000000003606e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: Modules linked in: CR2: 00000000386aae88 ---[ end trace a8bfbd202e712834 ]---
Let's fix this by remapping text and rodata individually, and leave the gaps mapped read-write.
Fixes: d9e3d2c4f10320 ("efi/x86: Don't map the entire kernel text RW for mixed mode") Reported-by: Jiri Slaby jslaby@suse.cz Tested-by: Jiri Slaby jslaby@suse.cz Signed-off-by: Ard Biesheuvel ardb@kernel.org Signed-off-by: Ingo Molnar mingo@kernel.org Link: https://lore.kernel.org/r/20200409130434.6736-10-ardb@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/platform/efi/efi_64.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-)
--- a/arch/x86/platform/efi/efi_64.c +++ b/arch/x86/platform/efi/efi_64.c @@ -202,7 +202,7 @@ virt_to_phys_or_null_size(void *va, unsi
int __init efi_setup_page_tables(unsigned long pa_memmap, unsigned num_pages) { - unsigned long pfn, text, pf; + unsigned long pfn, text, pf, rodata; struct page *page; unsigned npages; pgd_t *pgd = efi_mm.pgd; @@ -256,7 +256,7 @@ int __init efi_setup_page_tables(unsigne
efi_scratch.phys_stack = page_to_phys(page + 1); /* stack grows down */
- npages = (__end_rodata_aligned - _text) >> PAGE_SHIFT; + npages = (_etext - _text) >> PAGE_SHIFT; text = __pa(_text); pfn = text >> PAGE_SHIFT;
@@ -266,6 +266,14 @@ int __init efi_setup_page_tables(unsigne return 1; }
+ npages = (__end_rodata - __start_rodata) >> PAGE_SHIFT; + rodata = __pa(__start_rodata); + pfn = rodata >> PAGE_SHIFT; + if (kernel_map_pages_in_pgd(pgd, pfn, rodata, npages, pf)) { + pr_err("Failed to map kernel rodata 1:1\n"); + return 1; + } + return 0; }