Fix memmap.Translation.Perms returns.

memmap.Mappable.Translate() is passed a hostarch.AccessType indicating what
permissions are *immediately* required; it returns permissions in
memmap.Translation.Perms that are granted *to MM* until invalidation. MM
ensures that the permissions granted to the application are the intersection of
those granted by Translate, and those granted by VMA permissions; see
determination of pma.effectivePerms in
mm.MemoryManager.getPMAsInternalLocked(). This mechanism is used to avoid
marking pages dirty in the sentry's page cache for gofer-backed files until
PROT_WRITE pages are actually written to; see gofer.dentry.Translate(). In most
other cases, granting all supported permissions (to MM) up-front avoids a
redundant page fault for pages that are touched first for reading, and later
for writing.

Also:

- Prevent PROT_WRITE mappings of erofs files at mmap()/mprotect() time, rather
  than raising SIGBUS when writing to such mappings.

- Map nvproxy.frontendFD with PlatformEffectPopulate. This is the original goal
  of this CL; however, before this rest of this CL, MM.MMap() =>
  MM.populateVMAAndUnlock() => MM.getPMAsLocked(at=hostarch.NoAccess) =>
  MM.getPMAsInternalLocked(at=hostarch.NoAccess) =>
  nvproxy.frontendFD.Translate(at=hostarch.NoAccess) returns Translations with
  no permissions, causing MM.mapASLocked() to no-op.

PiperOrigin-RevId: 679360594

pkg/sentry/devices/nvproxy/frontend_mmap.go

@@ -23,6 +23,12 @@ import (
 
 // ConfigureMMap implements vfs.FileDescriptionImpl.ConfigureMMap.
 func (fd *frontendFD) ConfigureMMap(ctx context.Context, opts *memmap.MMapOpts) error {
+	// Nvidia kernel driver: kernel-open/nvidia/nv-mmap.c:nvidia_mmap_helper()
+	// requires vm_pgoff == 0, so trying to lazily fault any subset of the
+	// mapping that doesn't include the beginning will fail.
+	if opts.PlatformEffect < memmap.PlatformEffectPopulate {
+		opts.PlatformEffect = memmap.PlatformEffectPopulate
+	}
 	return vfs.GenericConfigureMMap(&fd.vfsfd, fd, opts)
 }
 
@@ -47,7 +53,7 @@ func (fd *frontendFD) Translate(ctx context.Context, required, optional memmap.M
 			Source: optional,
 			File:   &fd.memmapFile,
 			Offset: optional.Start,
-			Perms:  at,
+			Perms:  hostarch.AnyAccess,
 		},
 	}, nil
 }

pkg/sentry/devices/nvproxy/uvm_mmap.go

@@ -54,9 +54,7 @@ func (fd *uvmFD) Translate(ctx context.Context, required, optional memmap.Mappab
 			Source: optional,
 			File:   &fd.memmapFile,
 			Offset: optional.Start,
-			// kernel-open/nvidia-uvm/uvm.c:uvm_mmap() requires mappings to be
-			// PROT_READ|PROT_WRITE.
-			Perms: hostarch.ReadWrite,
+			Perms:  hostarch.AnyAccess,
 		},
 	}, nil
 }

pkg/sentry/devices/tpuproxy/accel/accel_fd_mmap.go

@@ -50,7 +50,7 @@ func (fd *accelFD) Translate(ctx context.Context, required, optional memmap.Mapp
 			Source: optional,
 			File:   &fd.memmapFile,
 			Offset: optional.Start,
-			Perms:  at,
+			Perms:  hostarch.AnyAccess,
 		},
 	}, nil
 }

pkg/sentry/devices/tpuproxy/vfio/pci_device_fd_mmap.go

@@ -61,7 +61,7 @@ func (fd *pciDeviceFD) Translate(ctx context.Context, required, optional memmap.
 			Source: optional,
 			File:   &fd.memmapFile,
 			Offset: optional.Start,
-			Perms:  at,
+			Perms:  hostarch.AnyAccess,
 		},
 	}, nil
 }

pkg/sentry/devices/tpuproxy/vfio/tpu_fd_mmap.go

@@ -50,7 +50,7 @@ func (fd *tpuFD) Translate(ctx context.Context, required, optional memmap.Mappab
 			Source: optional,
 			File:   &fd.memmapFile,
 			Offset: optional.Start,
-			Perms:  at,
+			Perms:  hostarch.AnyAccess,
 		},
 	}, nil
 }

pkg/sentry/devices/tpuproxy/vfio/vfio_fd_mmap.go

@@ -50,7 +50,7 @@ func (fd *vfioFD) Translate(ctx context.Context, required, optional memmap.Mappa
 			Source: optional,
 			File:   &fd.memmapFile,
 			Offset: optional.Start,
-			Perms:  at,
+			Perms:  hostarch.AnyAccess,
 		},
 	}, nil
 }

pkg/sentry/fsimpl/erofs/BUILD

@@ -61,6 +61,7 @@ go_library(
         "//pkg/errors/linuxerr",
         "//pkg/fspath",
         "//pkg/hostarch",
+        "//pkg/log",
         "//pkg/refs",
         "//pkg/safemem",
         "//pkg/sentry/fsimpl/lock",

pkg/sentry/fsimpl/erofs/regular_file.go

@@ -23,6 +23,7 @@ import (
 	"gvisor.dev/gvisor/pkg/erofs"
 	"gvisor.dev/gvisor/pkg/errors/linuxerr"
 	"gvisor.dev/gvisor/pkg/hostarch"
+	"gvisor.dev/gvisor/pkg/log"
 	"gvisor.dev/gvisor/pkg/safemem"
 	"gvisor.dev/gvisor/pkg/sentry/memmap"
 	"gvisor.dev/gvisor/pkg/sentry/vfs"
@@ -126,6 +127,9 @@ func (fd *regularFileFD) Seek(ctx context.Context, offset int64, whence int32) (
 
 // ConfigureMMap implements vfs.FileDescriptionImpl.ConfigureMMap.
 func (fd *regularFileFD) ConfigureMMap(ctx context.Context, opts *memmap.MMapOpts) error {
+	if opts.MaxPerms.Write && !opts.Private {
+		return linuxerr.EINVAL
+	}
 	return vfs.GenericConfigureMMap(&fd.vfsfd, fd.inode(), opts)
 }
 
@@ -163,6 +167,10 @@ func (i *inode) Translate(ctx context.Context, required, optional memmap.Mappabl
 		optional.End = pgend
 	}
 	if at.Write {
+		// This shouldn't be possible due to the check in ConfigureMMap().
+		inodeTranslateWriteWarnOnce.Do(func() {
+			log.Traceback("erofs.inode.Translate: unexpected access type %v", at)
+		})
 		return nil, &memmap.BusError{linuxerr.EROFS}
 	}
 	offset, err := i.DataOffset()
@@ -175,11 +183,13 @@ func (i *inode) Translate(ctx context.Context, required, optional memmap.Mappabl
 			Source: mr,
 			File:   &i.fs.mf,
 			Offset: mr.Start + offset,
-			Perms:  at,
+			Perms:  hostarch.ReadExecute,
 		},
 	}, nil
 }
 
+var inodeTranslateWriteWarnOnce sync.Once
+
 // InvalidateUnsavable implements memmap.Mappable.InvalidateUnsavable.
 func (i *inode) InvalidateUnsavable(ctx context.Context) error {
 	i.mapsMu.Lock()

pkg/sentry/fsimpl/gofer/regular_file.go

@@ -809,10 +809,7 @@ func (d *dentry) Translate(ctx context.Context, required, optional memmap.Mappab
 		segMR := seg.Range().Intersect(optional)
 		// TODO(jamieliu): Make Translations writable even if writability is
 		// not required if already kept-dirty by another writable translation.
-		perms := hostarch.AccessType{
-			Read:    true,
-			Execute: true,
-		}
+		perms := hostarch.ReadExecute
 		if at.Write {
 			// From this point forward, this memory can be dirtied through the
 			// mapping at any time.

pkg/sentry/fsimpl/iouringfs/iouringfs.go

@@ -570,7 +570,7 @@ func (sqemf *sqEntriesFile) Translate(ctx context.Context, required, optional me
 				Source: source,
 				File:   pgalloc.MemoryFileFromContext(ctx),
 				Offset: sqemf.fr.Start + source.Start,
-				Perms:  at,
+				Perms:  hostarch.AnyAccess,
 			},
 		}, nil
 	}
@@ -616,7 +616,7 @@ func (rbmf *ringsBufferFile) Translate(ctx context.Context, required, optional m
 				Source: source,
 				File:   pgalloc.MemoryFileFromContext(ctx),
 				Offset: rbmf.fr.Start + source.Start,
-				Perms:  at,
+				Perms:  hostarch.AnyAccess,
 			},
 		}, nil
 	}