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* [PATCH AUTOSEL 6.12 01/28] bpf: unify VM_WRITE vs VM_MAYWRITE use in BPF map mmaping logic
@ 2025-02-24 11:17 Sasha Levin
  2025-02-24 11:17 ` [PATCH AUTOSEL 6.12 02/28] selftests/bpf: Fix invalid flag of recv() Sasha Levin
                   ` (26 more replies)
  0 siblings, 27 replies; 29+ messages in thread
From: Sasha Levin @ 2025-02-24 11:17 UTC (permalink / raw)
  To: linux-kernel, stable
  Cc: Andrii Nakryiko, Jann Horn, Suren Baghdasaryan, Shakeel Butt,
	Alexei Starovoitov, Sasha Levin, daniel, bpf

From: Andrii Nakryiko <andrii@kernel.org>

[ Upstream commit 98671a0fd1f14e4a518ee06b19037c20014900eb ]

For all BPF maps we ensure that VM_MAYWRITE is cleared when
memory-mapping BPF map contents as initially read-only VMA. This is
because in some cases BPF verifier relies on the underlying data to not
be modified afterwards by user space, so once something is mapped
read-only, it shouldn't be re-mmap'ed as read-write.

As such, it's not necessary to check VM_MAYWRITE in bpf_map_mmap() and
map->ops->map_mmap() callbacks: VM_WRITE should be consistently set for
read-write mappings, and if VM_WRITE is not set, there is no way for
user space to upgrade read-only mapping to read-write one.

This patch cleans up this VM_WRITE vs VM_MAYWRITE handling within
bpf_map_mmap(), which is an entry point for any BPF map mmap()-ing
logic. We also drop unnecessary sanitization of VM_MAYWRITE in BPF
ringbuf's map_mmap() callback implementation, as it is already performed
by common code in bpf_map_mmap().

Note, though, that in bpf_map_mmap_{open,close}() callbacks we can't
drop VM_MAYWRITE use, because it's possible (and is outside of
subsystem's control) to have initially read-write memory mapping, which
is subsequently dropped to read-only by user space through mprotect().
In such case, from BPF verifier POV it's read-write data throughout the
lifetime of BPF map, and is counted as "active writer".

But its VMAs will start out as VM_WRITE|VM_MAYWRITE, then mprotect() can
change it to just VM_MAYWRITE (and no VM_WRITE), so when its finally
munmap()'ed and bpf_map_mmap_close() is called, vm_flags will be just
VM_MAYWRITE, but we still need to decrement active writer count with
bpf_map_write_active_dec() as it's still considered to be a read-write
mapping by the rest of BPF subsystem.

Similar reasoning applies to bpf_map_mmap_open(), which is called
whenever mmap(), munmap(), and/or mprotect() forces mm subsystem to
split original VMA into multiple discontiguous VMAs.

Memory-mapping handling is a bit tricky, yes.

Cc: Jann Horn <jannh@google.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20250129012246.1515826-1-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 kernel/bpf/ringbuf.c |  4 ----
 kernel/bpf/syscall.c | 10 ++++++++--
 2 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/kernel/bpf/ringbuf.c b/kernel/bpf/ringbuf.c
index e1cfe890e0be6..1499d8caa9a35 100644
--- a/kernel/bpf/ringbuf.c
+++ b/kernel/bpf/ringbuf.c
@@ -268,8 +268,6 @@ static int ringbuf_map_mmap_kern(struct bpf_map *map, struct vm_area_struct *vma
 		/* allow writable mapping for the consumer_pos only */
 		if (vma->vm_pgoff != 0 || vma->vm_end - vma->vm_start != PAGE_SIZE)
 			return -EPERM;
-	} else {
-		vm_flags_clear(vma, VM_MAYWRITE);
 	}
 	/* remap_vmalloc_range() checks size and offset constraints */
 	return remap_vmalloc_range(vma, rb_map->rb,
@@ -289,8 +287,6 @@ static int ringbuf_map_mmap_user(struct bpf_map *map, struct vm_area_struct *vma
 			 * position, and the ring buffer data itself.
 			 */
 			return -EPERM;
-	} else {
-		vm_flags_clear(vma, VM_MAYWRITE);
 	}
 	/* remap_vmalloc_range() checks size and offset constraints */
 	return remap_vmalloc_range(vma, rb_map->rb, vma->vm_pgoff + RINGBUF_PGOFF);
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 368ae8d231d41..fa43f26ce0dac 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -966,15 +966,21 @@ static int bpf_map_mmap(struct file *filp, struct vm_area_struct *vma)
 	vma->vm_ops = &bpf_map_default_vmops;
 	vma->vm_private_data = map;
 	vm_flags_clear(vma, VM_MAYEXEC);
+	/* If mapping is read-only, then disallow potentially re-mapping with
+	 * PROT_WRITE by dropping VM_MAYWRITE flag. This VM_MAYWRITE clearing
+	 * means that as far as BPF map's memory-mapped VMAs are concerned,
+	 * VM_WRITE and VM_MAYWRITE and equivalent, if one of them is set,
+	 * both should be set, so we can forget about VM_MAYWRITE and always
+	 * check just VM_WRITE
+	 */
 	if (!(vma->vm_flags & VM_WRITE))
-		/* disallow re-mapping with PROT_WRITE */
 		vm_flags_clear(vma, VM_MAYWRITE);
 
 	err = map->ops->map_mmap(map, vma);
 	if (err)
 		goto out;
 
-	if (vma->vm_flags & VM_MAYWRITE)
+	if (vma->vm_flags & VM_WRITE)
 		bpf_map_write_active_inc(map);
 out:
 	mutex_unlock(&map->freeze_mutex);
-- 
2.39.5


^ permalink raw reply related	[flat|nested] 29+ messages in thread

end of thread, other threads:[~2025-02-24 17:53 UTC | newest]

Thread overview: 29+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2025-02-24 11:17 [PATCH AUTOSEL 6.12 01/28] bpf: unify VM_WRITE vs VM_MAYWRITE use in BPF map mmaping logic Sasha Levin
2025-02-24 11:17 ` [PATCH AUTOSEL 6.12 02/28] selftests/bpf: Fix invalid flag of recv() Sasha Levin
2025-02-24 11:17 ` [PATCH AUTOSEL 6.12 03/28] ASoC: Intel: sof_sdw: Add lookup of quirk using PCI subsystem ID Sasha Levin
2025-02-24 11:17 ` [PATCH AUTOSEL 6.12 04/28] ASoC: Intel: sof_sdw: Add quirk for Asus Zenbook S14 Sasha Levin
2025-02-24 11:17 ` [PATCH AUTOSEL 6.12 05/28] ASoC: Intel: soc-acpi-intel-mtl-match: declare adr as ull Sasha Levin
2025-02-24 11:17 ` [PATCH AUTOSEL 6.12 06/28] ASoC: simple-card-utils.c: add missing dlc->of_node Sasha Levin
2025-02-24 11:17 ` [PATCH AUTOSEL 6.12 07/28] ALSA: hda/realtek: Limit mic boost on Positivo ARN50 Sasha Levin
2025-02-24 11:17 ` [PATCH AUTOSEL 6.12 08/28] ASoC: rsnd: indicate unsupported clock rate Sasha Levin
2025-02-24 11:17 ` [PATCH AUTOSEL 6.12 09/28] ASoC: rsnd: don't indicate warning on rsnd_kctrl_accept_runtime() Sasha Levin
2025-02-24 11:17 ` [PATCH AUTOSEL 6.12 10/28] ASoC: rsnd: adjust convert rate limitation Sasha Levin
2025-02-24 11:17 ` [PATCH AUTOSEL 6.12 11/28] ASoC: arizona/madera: use fsleep() in up/down DAPM event delays Sasha Levin
2025-02-24 11:17 ` [PATCH AUTOSEL 6.12 12/28] ASoC: SOF: Intel: hda: add softdep pre to snd-hda-codec-hdmi module Sasha Levin
2025-02-24 11:17 ` [PATCH AUTOSEL 6.12 13/28] PCI: pci_ids: add INTEL_HDA_PTL_H Sasha Levin
2025-02-24 11:17 ` [PATCH AUTOSEL 6.12 14/28] ALSA: hda: intel-dsp-config: Add PTL-H support Sasha Levin
2025-02-24 11:17 ` [PATCH AUTOSEL 6.12 15/28] ASoC: SOF: Intel: pci-ptl: Add support for PTL-H Sasha Levin
2025-02-24 11:17 ` [PATCH AUTOSEL 6.12 16/28] ALSA: hda: hda-intel: add Panther Lake-H support Sasha Levin
2025-02-24 11:17 ` [PATCH AUTOSEL 6.12 17/28] ASoC: SOF: amd: Add post_fw_run_delay ACP quirk Sasha Levin
2025-02-24 11:17 ` [PATCH AUTOSEL 6.12 18/28] ASoC: SOF: amd: Handle IPC replies before FW_BOOT_COMPLETE Sasha Levin
2025-02-24 11:17 ` [PATCH AUTOSEL 6.12 19/28] net: wwan: mhi_wwan_mbim: Silence sequence number glitch errors Sasha Levin
2025-02-24 11:17 ` [PATCH AUTOSEL 6.12 20/28] io-wq: backoff when retrying worker creation Sasha Levin
2025-02-24 11:17 ` [PATCH AUTOSEL 6.12 21/28] nvme-pci: quirk Acer FA100 for non-uniqueue identifiers Sasha Levin
2025-02-24 11:17 ` [PATCH AUTOSEL 6.12 22/28] nvme-tcp: add basic support for the C2HTermReq PDU Sasha Levin
2025-02-24 11:17 ` [PATCH AUTOSEL 6.12 23/28] nvmet-rdma: recheck queue state is LIVE in state lock in recv done Sasha Levin
2025-02-24 11:17 ` [PATCH AUTOSEL 6.12 24/28] apple-nvme: Release power domains when probe fails Sasha Levin
2025-02-24 11:17 ` [PATCH AUTOSEL 6.12 25/28] cifs: Treat unhandled directory name surrogate reparse points as mount directory nodes Sasha Levin
2025-02-24 17:52   ` Pali Rohár
2025-02-24 11:17 ` [PATCH AUTOSEL 6.12 26/28] sctp: Fix undefined behavior in left shift operation Sasha Levin
2025-02-24 11:17 ` [PATCH AUTOSEL 6.12 27/28] nvme: only allow entering LIVE from CONNECTING state Sasha Levin
2025-02-24 11:17 ` [PATCH AUTOSEL 6.12 28/28] irqchip/qcom-pdc: Workaround hardware register bug on X1E80100 Sasha Levin

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