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mm: Add 'mprotect' hook to struct vm_operations_struct
Background ========== 1. SGX enclave pages are populated with data by copying from normal memory via ioctl() (SGX_IOC_ENCLAVE_ADD_PAGES), which will be added later in this series. 2. It is desirable to be able to restrict those normal memory data sources. For instance, to ensure that the source data is executable before copying data to an executable enclave page. 3. Enclave page permissions are dynamic (just like normal permissions) and can be adjusted at runtime with mprotect(). This creates a problem because the original data source may have long since vanished at the time when enclave page permissions are established (mmap() or mprotect()). The solution (elsewhere in this series) is to force enclave creators to declare their paging permission *intent* up front to the ioctl(). This intent can be immediately compared to the source data’s mapping and rejected if necessary. The “intent” is also stashed off for later comparison with enclave PTEs. This ensures that any future mmap()/mprotect() operations performed by the enclave creator or done on behalf of the enclave can be compared with the earlier declared permissions. Problem ======= There is an existing mmap() hook which allows SGX to perform this permission comparison at mmap() time. However, there is no corresponding ->mprotect() hook. Solution ======== Add a vm_ops->mprotect() hook so that mprotect() operations which are inconsistent with any page's stashed intent can be rejected by the driver. Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com> Co-developed-by: Jarkko Sakkinen <jarkko@kernel.org> Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org> Signed-off-by: Borislav Petkov <bp@suse.de> Acked-by: Jethro Beekman <jethro@fortanix.com> Acked-by: Dave Hansen <dave.hansen@intel.com> Acked-by: Mel Gorman <mgorman@techsingularity.net> Acked-by: Hillf Danton <hdanton@sina.com> Cc: linux-mm@kvack.org Link: https://lkml.kernel.org/r/20201112220135.165028-11-jarkko@kernel.org
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2 changed files with 14 additions and 0 deletions
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@ -559,6 +559,13 @@ struct vm_operations_struct {
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void (*close)(struct vm_area_struct * area);
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int (*split)(struct vm_area_struct * area, unsigned long addr);
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int (*mremap)(struct vm_area_struct * area);
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/*
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* Called by mprotect() to make driver-specific permission
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* checks before mprotect() is finalised. The VMA must not
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* be modified. Returns 0 if eprotect() can proceed.
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*/
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int (*mprotect)(struct vm_area_struct *vma, unsigned long start,
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unsigned long end, unsigned long newflags);
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vm_fault_t (*fault)(struct vm_fault *vmf);
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vm_fault_t (*huge_fault)(struct vm_fault *vmf,
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enum page_entry_size pe_size);
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@ -616,9 +616,16 @@ static int do_mprotect_pkey(unsigned long start, size_t len,
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tmp = vma->vm_end;
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if (tmp > end)
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tmp = end;
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if (vma->vm_ops && vma->vm_ops->mprotect)
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error = vma->vm_ops->mprotect(vma, nstart, tmp, newflags);
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if (error)
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goto out;
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error = mprotect_fixup(vma, &prev, nstart, tmp, newflags);
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if (error)
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goto out;
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nstart = tmp;
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if (nstart < prev->vm_end)
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