Re: [RESEND PATCH] cxl/features: Ensure that count is set before access to end[] __counted_by()

[Dave Jiang <dave.jiang@intel.com>]

On 9/11/26 2:53 PM, Ashok Raj wrote:
> get_supported_features() assigns entries->num_features only after the
> memcpy() loop that fills entries->ent[] has already run. Since ent[]
> is __counted_by(num_features), the compiler's bounds instrumentation
> sees a 0-length array during that loop and FORTIFY_SOURCE trips on
> the memcpy. Set @num_features right after allocation, before any
> write into ent[], so the bound is correct for the whole lifetime of
> the array.
> 
> This was found via a fortify panic:
> 
>  memcpy: detected buffer overflow: 384 byte write of buffer size 0
>  WARNING: lib/string_helpers.c:1035 at __fortify_report+0x54/0xa0
>  kernel BUG at lib/string_helpers.c:1043!
>  Call trace:
>   __fortify_panic+0x10/0x18
>   get_supported_features.isra.0+0x4a0/0x4d0 [cxl_core]
>   devm_cxl_setup_features+0x84/0x120 [cxl_core]
>   cxl_pci_probe+0x254/0x5e0 [cxl_pci]
> 
> Same class of bug, same fix shape as commit 6c9d2e87df40
> ("cxl/fwctl: Fix __fortify_panic"), which fixed the analogous issue
> in cxlctl_get_supported_features() but missed this one.
> 
> Fixes: f0e6a2329bf9 ("cxl: Add Get Supported Features command for kernel usage")
> Signed-off-by: Ashok Raj <ashok.raj@oss.qualcomm.com>

Fixed title typo

Applied to cxl/next:
2cad1223081f

> ---
> RESEND: Dropped the mailing lists (linux-cxl, linux-kernel) from Cc
> by mistake on the first send. Resending with proper Cc.
> 
>  drivers/cxl/core/features.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/cxl/core/features.c b/drivers/cxl/core/features.c
> index ba6d2a5acb74..754fe5eb4b76 100644
> --- a/drivers/cxl/core/features.c
> +++ b/drivers/cxl/core/features.c
> @@ -97,6 +97,7 @@ get_supported_features(struct cxl_features_state *cxlfs)
>  		kvmalloc_flex(*entries, ent, count);
>  	if (!entries)
>  		return NULL;
> +	entries->num_features = count;
>  
>  	struct cxl_mbox_get_sup_feats_out *mbox_out __free(kvfree) =
>  		kvmalloc(cxl_mbox->payload_size, GFP_KERNEL);
> @@ -174,7 +175,6 @@ get_supported_features(struct cxl_features_state *cxlfs)
>  		start += num_entries;
>  	} while (remain_feats);
>  
> -	entries->num_features = count;
>  	entries->num_user_features = user_feats;
>  
>  	return no_free_ptr(entries);