Re: [PATCH RFC] drm/msm: move VM_BIND op validation to Rust

[Rob Clark]

On Mon, Oct 26, 2026 at 4:40 AM Konrad Dybcio <konradybcio@xxxxxxxxxx> wrote:
>
> From: Konrad Dybcio <konrad.dybcio@xxxxxxxxxxxxxxxx>
>
> Much of the VM handling code is a headache to read and maintain.
> There's a soup of mixed-signedness/size types which need to be compared
> and added and getting that wrong in C is very easy.
>
> The "(range + obj_offset) > obj->size" check could wrap for a large
> obj_offset, which let an out-of-range map be accepted and then mapped
> as nothing. Oxidize it and use checked_add() to fix that.
>
> This commit is a "get the foot in the door" type change to make sure
> that folks building kernels for Qualcomm SoCs have their Rust setup
> ready. It may/should be extended to the wider mm code once the
> appropriate abstractions are finalized.
>
> Worth noting, the C UERR() macro expands to dev_dbg() and the Rust
> implementation for that currently doesn't support dynamic_debug.
>
> The DRM_BRIDGE dependency is dropped because including RUST exposed
> some spaghetti dependencies ending at DEBUGFS and it's enabled anyway.
>
> Signed-off-by: Konrad Dybcio <konrad.dybcio@xxxxxxxxxxxxxxxx>
> ---
> (if this is rejected we may just patch the C code).
>
> Notably, this will regress some ancient configurations:
> -- arch/arm/Kconfig
>     select HAVE_RUST if CPU_LITTLE_ENDIAN && CPU_32v7 && !KASAN
>
> Smoke-tested on Glymur
> ---
>  drivers/gpu/drm/msm/Kconfig        |   2 +-
>  drivers/gpu/drm/msm/Makefile       |   1 +
>  drivers/gpu/drm/msm/msm_gem_vma.c  |  66 +++------------
>  drivers/gpu/drm/msm/msm_vm_bind.h  |  16 ++++
>  drivers/gpu/drm/msm/msm_vm_bind.rs | 160 +++++++++++++++++++++++++++++++++++++
>  rust/uapi/uapi_helper.h            |   1 +
>  6 files changed, 188 insertions(+), 58 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/Kconfig b/drivers/gpu/drm/msm/Kconfig
> index ed1c4775d1e9..f5c4749f8e95 100644
> --- a/drivers/gpu/drm/msm/Kconfig
> +++ b/drivers/gpu/drm/msm/Kconfig
> @@ -3,6 +3,7 @@
>  config DRM_MSM
>         tristate "MSM DRM"
>         depends on DRM
> +       depends on RUST
>         depends on ARCH_QCOM || SOC_IMX5 || COMPILE_TEST
>         depends on COMMON_CLK
>         depends on IOMMU_SUPPORT
> @@ -63,7 +64,6 @@ config DRM_MSM_VALIDATE_XML
>  config DRM_MSM_KMS
>         def_bool n
>         depends on DRM_MSM
> -       select DRM_BRIDGE
>         select DRM_BRIDGE_CONNECTOR
>         select DRM_CLIENT_SELECTION
>         select DRM_DISPLAY_HELPER
> diff --git a/drivers/gpu/drm/msm/Makefile b/drivers/gpu/drm/msm/Makefile
> index 1e246616f83f..826759a820a0 100644
> --- a/drivers/gpu/drm/msm/Makefile
> +++ b/drivers/gpu/drm/msm/Makefile
> @@ -129,6 +129,7 @@ msm-y += \
>         msm_ringbuffer.o \
>         msm_submitqueue.o \
>         msm_syncobj.o \
> +       msm_vm_bind.o \
>         msm_gpu_tracepoints.o \
>
>  msm-$(CONFIG_DRM_MSM_KMS) += \
> diff --git a/drivers/gpu/drm/msm/msm_gem_vma.c b/drivers/gpu/drm/msm/msm_gem_vma.c
> index f687a629629d..3c453b034e8f 100644
> --- a/drivers/gpu/drm/msm/msm_gem_vma.c
> +++ b/drivers/gpu/drm/msm/msm_gem_vma.c
> @@ -14,6 +14,7 @@
>  #include "msm_gpu.h"
>  #include "msm_mmu.h"
>  #include "msm_syncobj.h"
> +#include "msm_vm_bind.h"
>
>  #define vm_dbg(fmt, ...) pr_debug("%s:%d: "fmt"\n", __func__, __LINE__, ##__VA_ARGS__)
>
> @@ -981,23 +982,12 @@ vm_bind_job_create(struct drm_device *dev, struct drm_file *file, struct drm_gpu
>         return job;
>  }
>
> -static bool invalid_alignment(uint64_t addr)
> -{
> -       /*
> -        * Technically this is about GPU alignment, not CPU alignment.  But
> -        * I've not seen any qcom SoC where the SMMU does not support the
> -        * CPU's smallest page size.
> -        */
> -       return !PAGE_ALIGNED(addr);
> -}
> -
>  static int
>  lookup_op(struct msm_vm_bind_job *job, const struct drm_msm_vm_bind_op *op)
>  {
>         struct drm_device *dev = job->vm->drm;
>         struct msm_drm_private *priv = dev->dev_private;
>         int i = job->nr_ops++;
> -       int ret = 0;
>
>         job->ops[i].op = op->op;
>         job->ops[i].handle = op->handle;
> @@ -1006,48 +996,11 @@ lookup_op(struct msm_vm_bind_job *job, const struct drm_msm_vm_bind_op *op)
>         job->ops[i].range = op->range;
>         job->ops[i].flags = op->flags;
>
> -       if (op->flags & ~MSM_VM_BIND_OP_FLAGS)
> -               ret = UERR(EINVAL, dev, "invalid flags: %x\n", op->flags);
> -
> -       if (invalid_alignment(op->iova))
> -               ret = UERR(EINVAL, dev, "invalid address: %016llx\n", op->iova);
> -
> -       if (invalid_alignment(op->obj_offset))
> -               ret = UERR(EINVAL, dev, "invalid bo_offset: %016llx\n", op->obj_offset);
> -
> -       if (invalid_alignment(op->range))
> -               ret = UERR(EINVAL, dev, "invalid range: %016llx\n", op->range);
> -
> -       if (!drm_gpuvm_range_valid(job->vm, op->iova, op->range))
> -               ret = UERR(EINVAL, dev, "invalid range: %016llx, %016llx\n", op->iova, op->range);
> -
> -       /*
> -        * MAP must specify a valid handle.  But the handle MBZ for
> -        * UNMAP or MAP_NULL.
> -        */
> -       if (op->op == MSM_VM_BIND_OP_MAP) {
> -               if (!op->handle)
> -                       ret = UERR(EINVAL, dev, "invalid handle\n");
> -       } else if (op->handle) {
> -               ret = UERR(EINVAL, dev, "handle must be zero\n");
> -       }
> -
> -       switch (op->op) {
> -       case MSM_VM_BIND_OP_MAP:
> -       case MSM_VM_BIND_OP_MAP_NULL:
> -       case MSM_VM_BIND_OP_UNMAP:
> -               break;
> -       default:
> -               ret = UERR(EINVAL, dev, "invalid op: %u\n", op->op);
> -               break;
> -       }
> -
> -       if ((op->op == MSM_VM_BIND_OP_MAP_NULL) &&
> -           !adreno_smmu_has_prr(priv->gpu)) {
> -               ret = UERR(EINVAL, dev, "PRR not supported\n");
> -       }
> -
> -       return ret;
> +       return msm_vm_bind_check_op(dev->dev, op->op, op->handle, op->obj_offset,
> +                                   op->iova, op->range, op->flags, PAGE_SIZE,
> +                                   drm_gpuvm_range_valid(job->vm, op->iova, op->range),
> +                                   op->op == MSM_VM_BIND_OP_MAP_NULL &&
> +                                   adreno_smmu_has_prr(priv->gpu));
>  }
>
>  /*
> @@ -1118,11 +1071,10 @@ vm_bind_job_lookup_ops(struct msm_vm_bind_job *job, struct drm_msm_vm_bind *args
>                 op->obj = obj;
>                 cnt++;
>
> -               if ((op->range + op->obj_offset) > obj->size) {
> -                       ret = UERR(EINVAL, dev, "invalid range: %016llx + %016llx > %016zx\n",
> -                                  op->range, op->obj_offset, obj->size);
> +               ret = msm_vm_bind_check_bo_range(dev->dev, op->obj_offset, op->range,
> +                                                obj->size);
> +               if (ret)

I think the ioctl surface area is a sensible place to start using
rust.. but seems like this patch could instead be a 1-ish line patch
to use check_add_overflow() here?

Big picture, I'm a bit more interested in the
goto-error-unwind-spagatti-monstors.  Even there, just using more
cleanup.h would be an improvement.

BR,
-R

>                         goto out_unlock;
> -               }
>         }
>
>         *nr_bos = cnt;
> diff --git a/drivers/gpu/drm/msm/msm_vm_bind.h b/drivers/gpu/drm/msm/msm_vm_bind.h
> new file mode 100644
> index 000000000000..e8aa6adb9181
> --- /dev/null
> +++ b/drivers/gpu/drm/msm/msm_vm_bind.h
> @@ -0,0 +1,16 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +
> +#ifndef __MSM_VM_BIND_H__
> +#define __MSM_VM_BIND_H__
> +
> +#include <linux/types.h>
> +
> +struct device;
> +
> +int msm_vm_bind_check_op(struct device *dev, u32 op, u32 handle,
> +                        u64 obj_offset, u64 iova, u64 range, u32 flags,
> +                        u64 page_size, bool range_valid, bool prr_supported);
> +int msm_vm_bind_check_bo_range(struct device *dev, u64 obj_offset, u64 range,
> +                              u64 obj_size);
> +
> +#endif /* __MSM_VM_BIND_H__ */
> diff --git a/drivers/gpu/drm/msm/msm_vm_bind.rs b/drivers/gpu/drm/msm/msm_vm_bind.rs
> new file mode 100644
> index 000000000000..164208e0a1b4
> --- /dev/null
> +++ b/drivers/gpu/drm/msm/msm_vm_bind.rs
> @@ -0,0 +1,160 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +//! VM_BIND operation validation for the MSM driver.
> +
> +use kernel::{
> +    bindings,
> +    device::Device,
> +    error::code::EINVAL,
> +    prelude::*,
> +    uapi, //
> +};
> +
> +/// Validates a single VM_BIND operation.
> +///
> +/// Returns 0 if the operation is valid. Otherwise logs the reason and returns
> +/// `-EINVAL`.
> +///
> +/// `page_size` is the granularity that `iova`, `obj_offset` and `range` must be
> +/// aligned to. It is the GPU's alignment rather than the CPU's, but no known qcom
> +/// SMMU lacks support for the CPU's smallest page size.
> +/// `range_valid` is the result of `drm_gpuvm_range_valid()` for this operation.
> +/// `prr_supported` is only consulted for `MSM_VM_BIND_OP_MAP_NULL`.
> +///
> +/// # Safety
> +///
> +/// `dev` must point to a live `struct device`.
> +#[no_mangle]
> +pub unsafe extern "C" fn msm_vm_bind_check_op(
> +    dev: *mut bindings::device,
> +    op: u32,
> +    handle: u32,
> +    obj_offset: u64,
> +    iova: u64,
> +    range: u64,
> +    flags: u32,
> +    page_size: u64,
> +    range_valid: bool,
> +    prr_supported: bool,
> +) -> c_int {
> +    // SAFETY: The caller guarantees that `dev` is a live `struct device`.
> +    let dev: &Device = unsafe { Device::from_raw(dev) };
> +
> +    match check_op(
> +        dev,
> +        op,
> +        handle,
> +        obj_offset,
> +        iova,
> +        range,
> +        flags,
> +        page_size,
> +        range_valid,
> +        prr_supported,
> +    ) {
> +        Ok(()) => 0,
> +        Err(e) => e.to_errno(),
> +    }
> +}
> +
> +fn check_op(
> +    dev: &Device,
> +    op: u32,
> +    handle: u32,
> +    obj_offset: u64,
> +    iova: u64,
> +    range: u64,
> +    flags: u32,
> +    page_size: u64,
> +    range_valid: bool,
> +    prr_supported: bool,
> +) -> Result {
> +    let aligned = |addr: u64| page_size.is_power_of_two() && (addr & (page_size - 1)) == 0;
> +
> +    if flags & !uapi::MSM_VM_BIND_OP_FLAGS != 0 {
> +        dev_dbg!(dev, "invalid flags: {:x}\n", flags);
> +        return Err(EINVAL);
> +    }
> +
> +    if !aligned(iova) {
> +        dev_dbg!(dev, "invalid address: {:016x}\n", iova);
> +        return Err(EINVAL);
> +    }
> +
> +    if !aligned(obj_offset) {
> +        dev_dbg!(dev, "invalid bo_offset: {:016x}\n", obj_offset);
> +        return Err(EINVAL);
> +    }
> +
> +    if !aligned(range) {
> +        dev_dbg!(dev, "invalid range: {:016x}\n", range);
> +        return Err(EINVAL);
> +    }
> +
> +    if !range_valid {
> +        dev_dbg!(dev, "invalid range: {:016x}, {:016x}\n", iova, range);
> +        return Err(EINVAL);
> +    }
> +
> +    // MAP must name a handle; UNMAP and MAP_NULL must not.
> +    match op {
> +        uapi::MSM_VM_BIND_OP_MAP => {
> +            if handle == 0 {
> +                dev_dbg!(dev, "invalid handle\n");
> +                return Err(EINVAL);
> +            }
> +        }
> +        uapi::MSM_VM_BIND_OP_UNMAP | uapi::MSM_VM_BIND_OP_MAP_NULL => {
> +            if handle != 0 {
> +                dev_dbg!(dev, "handle must be zero\n");
> +                return Err(EINVAL);
> +            }
> +        }
> +        _ => {
> +            dev_dbg!(dev, "invalid op: {}\n", op);
> +            return Err(EINVAL);
> +        }
> +    }
> +
> +    if op == uapi::MSM_VM_BIND_OP_MAP_NULL && !prr_supported {
> +        dev_dbg!(dev, "PRR not supported\n");
> +        return Err(EINVAL);
> +    }
> +
> +    Ok(())
> +}
> +
> +/// Checks that `[obj_offset, obj_offset + range)` lies within an object of
> +/// `obj_size` bytes.
> +///
> +/// Returns 0 if it does. Otherwise logs the reason and returns `-EINVAL`.
> +///
> +/// # Safety
> +///
> +/// `dev` must point to a live `struct device`.
> +#[no_mangle]
> +pub unsafe extern "C" fn msm_vm_bind_check_bo_range(
> +    dev: *mut bindings::device,
> +    obj_offset: u64,
> +    range: u64,
> +    obj_size: u64,
> +) -> c_int {
> +    // SAFETY: The caller guarantees that `dev` is a live `struct device`.
> +    let dev: &Device = unsafe { Device::from_raw(dev) };
> +
> +    let fits = obj_offset
> +        .checked_add(range)
> +        .is_some_and(|end| end <= obj_size);
> +
> +    if fits {
> +        return 0;
> +    }
> +
> +    dev_dbg!(
> +        dev,
> +        "invalid range: {:016x} + {:016x} > {:016x}\n",
> +        range,
> +        obj_offset,
> +        obj_size
> +    );
> +    EINVAL.to_errno()
> +}
> diff --git a/rust/uapi/uapi_helper.h b/rust/uapi/uapi_helper.h
> index 489748ef642c..38741220270a 100644
> --- a/rust/uapi/uapi_helper.h
> +++ b/rust/uapi/uapi_helper.h
> @@ -7,6 +7,7 @@
>   */
>
>  #include <uapi/drm/drm.h>
> +#include <uapi/drm/msm_drm.h>
>  #include <uapi/drm/nova_drm.h>
>  #include <uapi/drm/panthor_drm.h>
>  #include <uapi/linux/android/binder.h>
>
> ---
> base-commit: 20a33c6b6cbe7e4805dfb6cd68816937443aa148
> change-id: 20261026-topic-vm_bind_rs-5551b8014396
>
> Best regards,
> --
> Konrad Dybcio <konrad.dybcio@xxxxxxxxxxxxxxxx>
>