[PATCH 1/5] drm/xe/reg_sr: Remove register pool

[Matt Roper]

On Thu, Dec 05, 2024 at 10:22:36AM -0800, Lucas De Marchi wrote:
> That pool implementation doesn't really work: if the krealloc happens to
> move the memory and return another address, the entries in the xarray
> become invalid, leading to use-after-free later:
> 
> 	BUG: KASAN: slab-use-after-free in xe_reg_sr_apply_mmio+0x570/0x760 [xe]
> 	Read of size 4 at addr ffff8881244b2590 by task modprobe/2753
> 
> 	Allocated by task 2753:
> 	 kasan_save_stack+0x39/0x70
> 	 kasan_save_track+0x14/0x40
> 	 kasan_save_alloc_info+0x37/0x60
> 	 __kasan_kmalloc+0xc3/0xd0
> 	 __kmalloc_node_track_caller_noprof+0x200/0x6d0
> 	 krealloc_noprof+0x229/0x380
> 
> Simplify the code to fix the bug. A better pooling strategy may be added
> back later if needed.
> 
> Fixes: 6f9f4763bc94 ("drm/xe/reg_sr: Remove register pool")

Is this line right?  It seems to be referring to a non-existent patch
(or itself based on the title?).

Aside from the Fixes:,

        Reviewed-by: Matt Roper <matthew.d.roper at intel.com>


> Signed-off-by: Lucas De Marchi <lucas.demarchi at intel.com>
> ---
>  drivers/gpu/drm/xe/xe_reg_sr.c       | 31 ++++++----------------------
>  drivers/gpu/drm/xe/xe_reg_sr_types.h |  6 ------
>  2 files changed, 6 insertions(+), 31 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_reg_sr.c b/drivers/gpu/drm/xe/xe_reg_sr.c
> index e1a0e27cda14c..c13123008e903 100644
> --- a/drivers/gpu/drm/xe/xe_reg_sr.c
> +++ b/drivers/gpu/drm/xe/xe_reg_sr.c
> @@ -27,46 +27,27 @@
>  #include "xe_reg_whitelist.h"
>  #include "xe_rtp_types.h"
>  
> -#define XE_REG_SR_GROW_STEP_DEFAULT	16
> -
>  static void reg_sr_fini(struct drm_device *drm, void *arg)
>  {
>  	struct xe_reg_sr *sr = arg;
> +	struct xe_reg_sr_entry *entry;
> +	unsigned long reg;
> +
> +	xa_for_each(&sr->xa, reg, entry)
> +		kfree(entry);
>  
>  	xa_destroy(&sr->xa);
> -	kfree(sr->pool.arr);
> -	memset(&sr->pool, 0, sizeof(sr->pool));
>  }
>  
>  int xe_reg_sr_init(struct xe_reg_sr *sr, const char *name, struct xe_device *xe)
>  {
>  	xa_init(&sr->xa);
> -	memset(&sr->pool, 0, sizeof(sr->pool));
> -	sr->pool.grow_step = XE_REG_SR_GROW_STEP_DEFAULT;
>  	sr->name = name;
>  
>  	return drmm_add_action_or_reset(&xe->drm, reg_sr_fini, sr);
>  }
>  EXPORT_SYMBOL_IF_KUNIT(xe_reg_sr_init);
>  
> -static struct xe_reg_sr_entry *alloc_entry(struct xe_reg_sr *sr)
> -{
> -	if (sr->pool.used == sr->pool.allocated) {
> -		struct xe_reg_sr_entry *arr;
> -
> -		arr = krealloc_array(sr->pool.arr,
> -				     ALIGN(sr->pool.allocated + 1, sr->pool.grow_step),
> -				     sizeof(*arr), GFP_KERNEL);
> -		if (!arr)
> -			return NULL;
> -
> -		sr->pool.arr = arr;
> -		sr->pool.allocated += sr->pool.grow_step;
> -	}
> -
> -	return &sr->pool.arr[sr->pool.used++];
> -}
> -
>  static bool compatible_entries(const struct xe_reg_sr_entry *e1,
>  			       const struct xe_reg_sr_entry *e2)
>  {
> @@ -112,7 +93,7 @@ int xe_reg_sr_add(struct xe_reg_sr *sr,
>  		return 0;
>  	}
>  
> -	pentry = alloc_entry(sr);
> +	pentry = kmalloc(sizeof(*pentry), GFP_KERNEL);
>  	if (!pentry) {
>  		ret = -ENOMEM;
>  		goto fail;
> diff --git a/drivers/gpu/drm/xe/xe_reg_sr_types.h b/drivers/gpu/drm/xe/xe_reg_sr_types.h
> index ad48a52b824a1..ebe11f237fa26 100644
> --- a/drivers/gpu/drm/xe/xe_reg_sr_types.h
> +++ b/drivers/gpu/drm/xe/xe_reg_sr_types.h
> @@ -20,12 +20,6 @@ struct xe_reg_sr_entry {
>  };
>  
>  struct xe_reg_sr {
> -	struct {
> -		struct xe_reg_sr_entry *arr;
> -		unsigned int used;
> -		unsigned int allocated;
> -		unsigned int grow_step;
> -	} pool;
>  	struct xarray xa;
>  	const char *name;
>  
> -- 
> 2.47.0
> 

-- 
Matt Roper
Graphics Software Engineer
Linux GPU Platform Enablement
Intel Corporation