Messages in this thread Patch in this message | | | Date | Sun, 30 Apr 2006 19:29:59 +0200 | From | blaisorblade@yahoo ... | Subject | [patch 06/14] remap_file_pages protection support: enhance syscall interface |
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From: Ingo Molnar <mingo@elte.hu>, Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Enable the 'prot' parameter for shared-writable mappings (the ones which are the primary target for remap_file_pages), without breaking up the vma.
This contains simply the changes to the syscall code, based on Ingo's patch. Differently from his one, I've *not* added a new syscall, choosing to add a new flag (MAP_CHGPROT) which the application must specify to get the new behavior (prot != 0 is accepted and prot == 0 means PROT_NONE).
Upon Hugh's suggestion, simplify the permission checking on the VMA, reusing mprotect()'s trick.
Index: linux-2.6.git/mm/fremap.c =================================================================== --- linux-2.6.git.orig/mm/fremap.c +++ linux-2.6.git/mm/fremap.c @@ -4,6 +4,10 @@ * Explicit pagetable population and nonlinear (random) mappings support. * * started by Ingo Molnar, Copyright (C) 2002, 2003 + * + * support of nonuniform remappings: + * Copyright (C) 2004 Ingo Molnar + * Copyright (C) 2005 Paolo 'Blaisorblade' Giarrusso */ #include <linux/mm.h> @@ -126,18 +130,14 @@ out: * file within an existing vma. * @start: start of the remapped virtual memory range * @size: size of the remapped virtual memory range - * @prot: new protection bits of the range + * @prot: new protection bits of the range, must be 0 if not using MAP_CHGPROT * @pgoff: to be mapped page of the backing store file - * @flags: 0 or MAP_NONBLOCKED - the later will cause no IO. + * @flags: bits MAP_CHGPROT or MAP_NONBLOCKED - the later will cause no IO. * * this syscall works purely via pagetables, so it's the most efficient * way to map the same (large) file into a given virtual window. Unlike * mmap()/mremap() it does not create any new vmas. The new mappings are * also safe across swapout. - * - * NOTE: the 'prot' parameter right now is ignored, and the vma's default - * protection is used. Arbitrary protections might be implemented in the - * future. */ asmlinkage long sys_remap_file_pages(unsigned long start, unsigned long size, unsigned long prot, unsigned long pgoff, unsigned long flags) @@ -150,7 +150,7 @@ asmlinkage long sys_remap_file_pages(uns int has_write_lock = 0; pgprot_t pgprot; - if (prot) + if (prot && !(flags & MAP_CHGPROT)) goto out; /* * Sanitize the syscall parameters: @@ -193,7 +193,19 @@ retry: if (end <= start || start < vma->vm_start || end > vma->vm_end) goto out_unlock; - pgprot = vma->vm_page_prot; + if (flags & MAP_CHGPROT) { + unsigned long vm_prots = calc_vm_prot_bits(prot); + + /* vma->vm_flags >> 4 shifts VM_MAY% in place of VM_% */ + if ((vm_prots & ~(vma->vm_flags >> 4)) & + (VM_READ | VM_WRITE | VM_EXEC)) { + err = -EPERM; + goto out_unlock; + } + + pgprot = protection_map[vm_prots | VM_SHARED]; + } else + pgprot = vma->vm_page_prot; if (!vma->vm_private_data || (vma->vm_flags & VM_NONLINEAR)) { /* Must set VM_NONLINEAR before any pages are populated. */ @@ -215,6 +227,17 @@ retry: spin_unlock(&mapping->i_mmap_lock); } + if (pgprot_val(pgprot) != pgprot_val(vma->vm_page_prot) && + !(vma->vm_flags & VM_MANYPROTS)) { + if (!has_write_lock) { + up_read(&mm->mmap_sem); + down_write(&mm->mmap_sem); + has_write_lock = 1; + goto retry; + } + vma->vm_flags |= VM_MANYPROTS; + } + err = vma->vm_ops->populate(vma, start, size, pgprot, pgoff, flags & MAP_NONBLOCK); -- Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!". Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894) http://www.user-mode-linux.org/~blaisorblade - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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