x86/mm/pageattr: Introduce helper function to unmap EFI boot services (7e0dabd3) · Commits · 戴 / test

Ideally, after kernel assumes control of the platform, firmware shouldn't access EFI boot services code/data regions. But, it's noticed that this is not so true in many x86 platforms. Hence, during boot, kernel reserves EFI boot services code/data regions [1] and maps [2] them to efi_pgd so that call to set_virtual_address_map() doesn't fail. After returning from set_virtual_address_map(), kernel frees the reserved regions [3] but they still remain mapped. Hence, introduce kernel_unmap_pages_in_pgd() which will later be used to unmap EFI boot services code/data regions. While at it modify kernel_map_pages_in_pgd() by: 1. Adding __init modifier because it's always used *only* during boot. 2. Add a warning if it's used after SMP is initialized because it uses __flush_tlb_all() which flushes mappings only on current CPU. Unmapping EFI boot services code/data regions will result in clearing PAGE_PRESENT bit and it shouldn't bother L1TF cases because it's already handled by protnone_mask() at arch/x86/include/asm/pgtable-invert.h. [1] efi_reserve_boot_services() [2] efi_map_region() -> __map_region() -> kernel_map_pages_in_pgd() [3] efi_free_boot_services() Signed-off-by:

Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com> Signed-off-by:

Ard Biesheuvel <ard.biesheuvel@linaro.org> Reviewed-by:

Thomas Gleixner <tglx@linutronix.de> Cc: Andy Lutomirski <luto@kernel.org> Cc: Arend van Spriel <arend.vanspriel@broadcom.com> Cc: Bhupesh Sharma <bhsharma@redhat.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Eric Snowberg <eric.snowberg@oracle.com> Cc: Hans de Goede <hdegoede@redhat.com> Cc: Joe Perches <joe@perches.com> Cc: Jon Hunter <jonathanh@nvidia.com> Cc: Julien Thierry <julien.thierry@arm.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Marc Zyngier <marc.zyngier@arm.com> Cc: Matt Fleming <matt@codeblueprint.co.uk> Cc: Nathan Chancellor <natechancellor@gmail.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Sedat Dilek <sedat.dilek@gmail.com> Cc: YiFei Zhu <zhuyifei1999@gmail.com> Cc: linux-efi@vger.kernel.org Link: http://lkml.kernel.org/r/20181129171230.18699-5-ard.biesheuvel@linaro.org Signed-off-by:

Ingo Molnar <mingo@kernel.org>

arch/x86/include/asm/pgtable_types.h

+6 −2

Original line number	Diff line number	Diff line
		@@ -564,8 +564,12 @@ extern pte_t lookup_address_in_pgd(pgd_t pgd, unsigned long address,
		unsigned int *level);
		extern pmd_t *lookup_pmd_address(unsigned long address);
		extern phys_addr_t slow_virt_to_phys(void *__address);
		extern int kernel_map_pages_in_pgd(pgd_t *pgd, u64 pfn, unsigned long address,
		unsigned numpages, unsigned long page_flags);
		extern int __init kernel_map_pages_in_pgd(pgd_t *pgd, u64 pfn,
		unsigned long address,
		unsigned numpages,
		unsigned long page_flags);
		extern int __init kernel_unmap_pages_in_pgd(pgd_t *pgd, unsigned long address,
		unsigned long numpages);
		#endif /* !__ASSEMBLY__ */

		#endif /* _ASM_X86_PGTABLE_DEFS_H */

arch/x86/mm/pageattr.c

+38 −2

Original line number	Diff line number	Diff line
		@@ -2338,7 +2338,7 @@ bool kernel_page_present(struct page *page)

		#endif /* CONFIG_DEBUG_PAGEALLOC */

		int kernel_map_pages_in_pgd(pgd_t *pgd, u64 pfn, unsigned long address,
		int __init kernel_map_pages_in_pgd(pgd_t *pgd, u64 pfn, unsigned long address,
		unsigned numpages, unsigned long page_flags)
		{
		int retval = -EINVAL;
		@@ -2353,6 +2353,8 @@ int kernel_map_pages_in_pgd(pgd_t *pgd, u64 pfn, unsigned long address,
		.flags = 0,
		};

		WARN_ONCE(num_online_cpus() > 1, "Don't call after initializing SMP");

		if (!(__supported_pte_mask & _PAGE_NX))
		goto out;

		@@ -2374,6 +2376,40 @@ out:
		return retval;
		}

		/*
		* __flush_tlb_all() flushes mappings only on current CPU and hence this
		* function shouldn't be used in an SMP environment. Presently, it's used only
		* during boot (way before smp_init()) by EFI subsystem and hence is ok.
		*/
		int __init kernel_unmap_pages_in_pgd(pgd_t *pgd, unsigned long address,
		unsigned long numpages)
		{
		int retval;

		/*
		* The typical sequence for unmapping is to find a pte through
		* lookup_address_in_pgd() (ideally, it should never return NULL because
		* the address is already mapped) and change it's protections. As pfn is
		* the target of a mapping, it's not useful while unmapping.
		*/
		struct cpa_data cpa = {
		.vaddr = &address,
		.pfn = 0,
		.pgd = pgd,
		.numpages = numpages,
		.mask_set = __pgprot(0),
		.mask_clr = __pgprot(_PAGE_PRESENT \| _PAGE_RW),
		.flags = 0,
		};

		WARN_ONCE(num_online_cpus() > 1, "Don't call after initializing SMP");

		retval = __change_page_attr_set_clr(&cpa, 0);
		__flush_tlb_all();

		return retval;
		}

		/*
		* The testcases use internal knowledge of the implementation that shouldn't
		* be exposed to the rest of the kernel. Include these directly here.

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