diff options
Diffstat (limited to 'pkg/sentry/mm/syscalls.go')
| -rw-r--r-- | pkg/sentry/mm/syscalls.go | 50 |
1 files changed, 40 insertions, 10 deletions
diff --git a/pkg/sentry/mm/syscalls.go b/pkg/sentry/mm/syscalls.go index 0730be65b..21aeabde8 100644 --- a/pkg/sentry/mm/syscalls.go +++ b/pkg/sentry/mm/syscalls.go @@ -320,8 +320,21 @@ func (mm *MemoryManager) MRemap(ctx context.Context, oldAddr usermem.Addr, oldSi return 0, syserror.EFAULT } + // Behavior matrix: + // + // Move | oldSize = 0 | oldSize < newSize | oldSize = newSize | oldSize > newSize + // ---------+-------------+-------------------+-------------------+------------------ + // NoMove | ENOMEM [1] | Grow in-place | No-op | Shrink in-place + // MayMove | Copy [1] | Grow in-place or | No-op | Shrink in-place + // | | move | | + // MustMove | Copy | Move and grow | Move | Shrink and move + // + // [1] In-place growth is impossible because the vma at oldAddr already + // occupies at least part of the destination. Thus the NoMove case always + // fails and the MayMove case always falls back to copying. + if opts.Move != MRemapMustMove { - // Handle noops and in-place shrinking. These cases don't care if + // Handle no-ops and in-place shrinking. These cases don't care if // [oldAddr, oldEnd) maps to a single vma, or is even mapped at all // (aside from oldAddr). if newSize <= oldSize { @@ -363,15 +376,13 @@ func (mm *MemoryManager) MRemap(ctx context.Context, oldAddr usermem.Addr, oldSi return oldAddr, nil } // In-place growth failed. In the MRemapMayMove case, fall through to - // moving below. + // copying/moving below. if opts.Move == MRemapNoMove { return 0, err } } - // Handle moving, which is the only remaining case. - - // Find a destination for the move. + // Find a location for the new mapping. var newAR usermem.AddrRange switch opts.Move { case MRemapMayMove: @@ -399,7 +410,9 @@ func (mm *MemoryManager) MRemap(ctx context.Context, oldAddr usermem.Addr, oldSi mm.unmapLocked(ctx, newAR) // If the sizes specify shrinking, unmap everything between the new and - // old sizes at the source. + // old sizes at the source. Unmapping before the following checks is + // correct: compare Linux's mm/mremap.c:mremap_to() => do_munmap(), + // vma_to_resize(). if newSize < oldSize { oldNewEnd := oldAddr + usermem.Addr(newSize) mm.unmapLocked(ctx, usermem.AddrRange{oldNewEnd, oldEnd}) @@ -412,9 +425,6 @@ func (mm *MemoryManager) MRemap(ctx context.Context, oldAddr usermem.Addr, oldSi oldAR := usermem.AddrRange{oldAddr, oldEnd} - // In the MRemapMustMove case, these checks happen after unmapping: - // mm/mremap.c:mremap_to() => do_munmap(), vma_to_resize(). - // Check that oldEnd maps to the same vma as oldAddr. if vseg.End() < oldEnd { return 0, syserror.EFAULT @@ -431,12 +441,32 @@ func (mm *MemoryManager) MRemap(ctx context.Context, oldAddr usermem.Addr, oldSi if vma.off+uint64(newAR.Length()) < vma.off { return 0, syserror.EINVAL } - // Inform the Mappable, if any, of the copied mapping. + // Inform the Mappable, if any, of the new mapping. if err := vma.mappable.CopyMapping(ctx, mm, oldAR, newAR, vseg.mappableOffsetAt(oldAR.Start)); err != nil { return 0, err } } + if oldSize == 0 { + // Handle copying. + // + // We can't use createVMALocked because it calls Mappable.AddMapping, + // whereas we've already called Mappable.CopyMapping (which is + // consistent with Linux). Call vseg.Value() (rather than + // vseg.ValuePtr()) to make a copy of the vma. + vma := vseg.Value() + if vma.mappable != nil { + vma.off = vseg.mappableOffsetAt(oldAR.Start) + } + if vma.id != nil { + vma.id.IncRef() + } + mm.vmas.Add(newAR, vma) + return newAR.Start, nil + } + + // Handle moving. + // // Remove the existing vma before inserting the new one to minimize // iterator invalidation. We do this directly (instead of calling // removeVMAsLocked) because: |