Re: [PATCH] drm/i915/sseu: fix max_subslices array-index-out-of-bounds access

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 20/02/2023 17:18, Andrea Righi wrote:
> It seems that commit bc3c5e0809ae ("drm/i915/sseu: Don't try to store EU
> mask internally in UAPI format") exposed a potential out-of-bounds
> access, reported by UBSAN as following on a laptop with a gen 11 i915
> card:
> 
>    UBSAN: array-index-out-of-bounds in drivers/gpu/drm/i915/gt/intel_sseu.c:65:27
>    index 6 is out of range for type 'u16 [6]'
>    CPU: 2 PID: 165 Comm: systemd-udevd Not tainted 6.2.0-9-generic #9-Ubuntu
>    Hardware name: Dell Inc. XPS 13 9300/077Y9N, BIOS 1.11.0 03/22/2022
>    Call Trace:
>     <TASK>
>     show_stack+0x4e/0x61
>     dump_stack_lvl+0x4a/0x6f
>     dump_stack+0x10/0x18
>     ubsan_epilogue+0x9/0x3a
>     __ubsan_handle_out_of_bounds.cold+0x42/0x47
>     gen11_compute_sseu_info+0x121/0x130 [i915]
>     intel_sseu_info_init+0x15d/0x2b0 [i915]
>     intel_gt_init_mmio+0x23/0x40 [i915]
>     i915_driver_mmio_probe+0x129/0x400 [i915]
>     ? intel_gt_probe_all+0x91/0x2e0 [i915]
>     i915_driver_probe+0xe1/0x3f0 [i915]
>     ? drm_privacy_screen_get+0x16d/0x190 [drm]
>     ? acpi_dev_found+0x64/0x80
>     i915_pci_probe+0xac/0x1b0 [i915]
>     ...
> 
> According to the definition of sseu_dev_info, eu_mask->hsw is limited to
> a maximum of GEN_MAX_SS_PER_HSW_SLICE (6) sub-slices, but
> gen11_sseu_info_init() can potentially set 8 sub-slices, in the
> !IS_JSL_EHL(gt->i915) case.
> 
> Fix this by reserving up to 8 slots for max_subslices in the eu_mask
> struct.
> 
> Reported-by: Emil Renner Berthing <emil.renner.berthing@canonical.com>
> Signed-off-by: Andrea Righi <andrea.righi@canonical.com>

Looks like bug was probably introduced in:

Fixes: bc3c5e0809ae ("drm/i915/sseu: Don't try to store EU mask internally in UAPI format")
Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Balasubramani Vivekanandan <balasubramani.vivekanandan@intel.com>
Cc: <stable@vger.kernel.org> # v6.0+

Adding Matt to cross-check.

Regards,

Tvrtko

> ---
>   drivers/gpu/drm/i915/gt/intel_sseu.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/gt/intel_sseu.h b/drivers/gpu/drm/i915/gt/intel_sseu.h
> index aa87d3832d60..d7e8c374f153 100644
> --- a/drivers/gpu/drm/i915/gt/intel_sseu.h
> +++ b/drivers/gpu/drm/i915/gt/intel_sseu.h
> @@ -27,7 +27,7 @@ struct drm_printer;
>    * is only relevant to pre-Xe_HP platforms (Xe_HP and beyond use the
>    * I915_MAX_SS_FUSE_BITS value below).
>    */
> -#define GEN_MAX_SS_PER_HSW_SLICE	6
> +#define GEN_MAX_SS_PER_HSW_SLICE	8
>   
>   /*
>    * Maximum number of 32-bit registers used by hardware to express the