From 33a154a96e71a34a1bcca9f40da343dbbf7b38b4 Mon Sep 17 00:00:00 2001 From: Alexei Starovoitov Date: Thu, 1 Oct 2026 14:52:55 +0000 Subject: selftests/bpf: Test packet range of pointers sharing an id Add tests where two packet pointers share an id and tightening one pointer's umax from its var_off would put it less than their constant distance from the other's umax: with an index & 0x38 capped at 50, the base pointer keeps umax 50, so the pointer 8 bytes further on must keep umax 58, even though its known bits allow at most 56. These refused a valid program or accepted an out-of-bounds access before the fix: - check the advanced copy, load through the base: valid, was refused; - check the base, load the byte at base + 1 through a copy advanced by 8: was accepted; - check base + 4, load 4 bytes at base + 2 through base + 8: reads two bytes past the checked range, was accepted; - the same as the second with data_meta pointers checked against data: was accepted. These pass with and without the fix and cover nearby paths: - subtract an unknown scalar from a checked pointer and load below it (the range is kept across a new id); - reach a load through two paths whose checks cover 8 and 7 bytes after the loaded pointer; the second path must not be pruned by the first; - spill a copy of a pointer, check the pointer, fill the copy and load one byte past the checked range: the load is refused, and the copy has the range of the check. Signed-off-by: Alexei Starovoitov Link: https://lore.kernel.org/bpf/20261001145255.855630-2-alexei.starovoitov@gmail.com Signed-off-by: Kumar Kartikeya Dwivedi --- Documentation/driver-api/sync_file.rst | 86 ++++++++++++++++++++++++++++++++++ 1 file changed, 86 insertions(+) create mode 100644 Documentation/driver-api/sync_file.rst (limited to 'Documentation/driver-api/sync_file.rst') diff --git a/Documentation/driver-api/sync_file.rst b/Documentation/driver-api/sync_file.rst new file mode 100644 index 000000000..496fb2c3b --- /dev/null +++ b/Documentation/driver-api/sync_file.rst @@ -0,0 +1,86 @@ +=================== +Sync File API Guide +=================== + +:Author: Gustavo Padovan + +This document serves as a guide for device drivers writers on what the +sync_file API is, and how drivers can support it. Sync file is the carrier of +the fences(struct dma_fence) that are needed to synchronize between drivers or +across process boundaries. + +The sync_file API is meant to be used to send and receive fence information +to/from userspace. It enables userspace to do explicit fencing, where instead +of attaching a fence to the buffer a producer driver (such as a GPU or V4L +driver) sends the fence related to the buffer to userspace via a sync_file. + +The sync_file then can be sent to the consumer (DRM driver for example), that +will not use the buffer for anything before the fence(s) signals, i.e., the +driver that issued the fence is not using/processing the buffer anymore, so it +signals that the buffer is ready to use. And vice-versa for the consumer -> +producer part of the cycle. + +Sync files allows userspace awareness on buffer sharing synchronization between +drivers. + +Sync file was originally added in the Android kernel but current Linux Desktop +can benefit a lot from it. + +in-fences and out-fences +------------------------ + +Sync files can go either to or from userspace. When a sync_file is sent from +the driver to userspace we call the fences it contains 'out-fences'. They are +related to a buffer that the driver is processing or is going to process, so +the driver creates an out-fence to be able to notify, through +dma_fence_signal(), when it has finished using (or processing) that buffer. +Out-fences are fences that the driver creates. + +On the other hand if the driver receives fence(s) through a sync_file from +userspace we call these fence(s) 'in-fences'. Receiving in-fences means that +we need to wait for the fence(s) to signal before using any buffer related to +the in-fences. + +Creating Sync Files +------------------- + +When a driver needs to send an out-fence userspace it creates a sync_file. + +Interface:: + + struct sync_file *sync_file_create(struct dma_fence *fence); + +The caller pass the out-fence and gets back the sync_file. That is just the +first step, next it needs to install an fd on sync_file->file. So it gets an +fd:: + + fd = get_unused_fd_flags(O_CLOEXEC); + +and installs it on sync_file->file:: + + fd_install(fd, sync_file->file); + +The sync_file fd now can be sent to userspace. + +If the creation process fail, or the sync_file needs to be released by any +other reason fput(sync_file->file) should be used. + +Receiving Sync Files from Userspace +----------------------------------- + +When userspace needs to send an in-fence to the driver it passes file descriptor +of the Sync File to the kernel. The kernel can then retrieve the fences +from it. + +Interface:: + + struct dma_fence *sync_file_get_fence(int fd); + + +The returned reference is owned by the caller and must be disposed of +afterwards using dma_fence_put(). In case of error, a NULL is returned instead. + +References: + +1. struct sync_file in include/linux/sync_file.h +2. All interfaces mentioned above defined in include/linux/sync_file.h -- cgit v1.3.1