path: root/arch/x86/platform/efi/efi_32.c
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authorMatt Fleming <matt@codeblueprint.co.uk>2015-11-27 21:09:34 +0000
committerIngo Molnar <mingo@kernel.org>2015-11-29 09:15:42 +0100
commit67a9108ed4313b85a9c53406d80dc1ae3f8c3e36 (patch)
treedeef46796dba57f2edf7b566abd67efff2283363 /arch/x86/platform/efi/efi_32.c
parentc9f2a9a65e4855b74d92cdad688f6ee4a1a323ff (diff)
x86/efi: Build our own page table structures
With commit e1a58320a38d ("x86/mm: Warn on W^X mappings") all users booting on 64-bit UEFI machines see the following warning, ------------[ cut here ]------------ WARNING: CPU: 7 PID: 1 at arch/x86/mm/dump_pagetables.c:225 note_page+0x5dc/0x780() x86/mm: Found insecure W+X mapping at address ffff88000005f000/0xffff88000005f000 ... x86/mm: Checked W+X mappings: FAILED, 165660 W+X pages found. ... This is caused by mapping EFI regions with RWX permissions. There isn't much we can do to restrict the permissions for these regions due to the way the firmware toolchains mix code and data, but we can at least isolate these mappings so that they do not appear in the regular kernel page tables. In commit d2f7cbe7b26a ("x86/efi: Runtime services virtual mapping") we started using 'trampoline_pgd' to map the EFI regions because there was an existing identity mapping there which we use during the SetVirtualAddressMap() call and for broken firmware that accesses those addresses. But 'trampoline_pgd' shares some PGD entries with 'swapper_pg_dir' and does not provide the isolation we require. Notably the virtual address for __START_KERNEL_map and MODULES_START are mapped by the same PGD entry so we need to be more careful when copying changes over in efi_sync_low_kernel_mappings(). This patch doesn't go the full mile, we still want to share some PGD entries with 'swapper_pg_dir'. Having completely separate page tables brings its own issues such as synchronising new mappings after memory hotplug and module loading. Sharing also keeps memory usage down. Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk> Reviewed-by: Borislav Petkov <bp@suse.de> Acked-by: Borislav Petkov <bp@suse.de> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Andy Lutomirski <luto@kernel.org> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Dave Jones <davej@codemonkey.org.uk> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com> Cc: Stephen Smalley <sds@tycho.nsa.gov> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Toshi Kani <toshi.kani@hp.com> Cc: linux-efi@vger.kernel.org Link: http://lkml.kernel.org/r/1448658575-17029-6-git-send-email-matt@codeblueprint.co.uk Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/x86/platform/efi/efi_32.c')
1 files changed, 5 insertions, 0 deletions
diff --git a/arch/x86/platform/efi/efi_32.c b/arch/x86/platform/efi/efi_32.c
index ed5b67338294..58d669bc8250 100644
--- a/arch/x86/platform/efi/efi_32.c
+++ b/arch/x86/platform/efi/efi_32.c
@@ -38,6 +38,11 @@
* say 0 - 3G.
+int __init efi_alloc_page_tables(void)
+ return 0;
void efi_sync_low_kernel_mappings(void) {}
void __init efi_dump_pagetable(void) {}
int __init efi_setup_page_tables(unsigned long pa_memmap, unsigned num_pages)

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