linux-hardening - [PATCH] drm/radeon: Remove __counted

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Message-Id: <20240529-drop-counted-by-radeon-states-state-array-v1-1-5cdc1fb29be7@kernel.org>
Date: Wed, 29 May 2024 14:54:44 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Alex Deucher <alexander.deucher@....com>, 
 Christian König <christian.koenig@....com>
Cc: Kees Cook <keescook@...omium.org>, 
 "Gustavo A. R. Silva" <gustavoars@...nel.org>, 
 Bill Wendling <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>, 
 amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org, 
 linux-hardening@...r.kernel.org, llvm@...ts.linux.dev, 
 patches@...ts.linux.dev, stable@...r.kernel.org, 
 Nathan Chancellor <nathan@...nel.org>
Subject: [PATCH] drm/radeon: Remove __counted_by from StateArray.states[]

From: Bill Wendling <morbo@...gle.com>

Work for __counted_by on generic pointers in structures (not just
flexible array members) has started landing in Clang 19 (current tip of
tree). During the development of this feature, a restriction was added
to __counted_by to prevent the flexible array member's element type from
including a flexible array member itself such as:

  struct foo {
    int count;
    char buf[];
  };

  struct bar {
    int count;
    struct foo data[] __counted_by(count);
  };

because the size of data cannot be calculated with the standard array
size formula:

  sizeof(struct foo) * count

This restriction was downgraded to a warning but due to CONFIG_WERROR,
it can still break the build. The application of __counted_by on the
states member of 'struct _StateArray' triggers this restriction,
resulting in:

  drivers/gpu/drm/radeon/pptable.h:442:5: error: 'counted_by' should not be applied to an array with element of unknown size because 'ATOM_PPLIB_STATE_V2' (aka 'struct _ATOM_PPLIB_STATE_V2') is a struct type with a flexible array member. This will be an error in a future compiler version [-Werror,-Wbounds-safety-counted-by-elt-type-unknown-size]
    442 |     ATOM_PPLIB_STATE_V2 states[] __counted_by(ucNumEntries);
        |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
  1 error generated.

Remove this use of __counted_by to fix the warning/error. However,
rather than remove it altogether, leave it commented, as it may be
possible to support this in future compiler releases.

Cc: stable@...r.kernel.org
Closes: https://github.com/ClangBuiltLinux/linux/issues/2028
Fixes: efade6fe50e7 ("drm/radeon: silence UBSAN warning (v3)")
Signed-off-by: Bill Wendling <morbo@...gle.com>
Co-developed-by: Nathan Chancellor <nathan@...nel.org>
Signed-off-by: Nathan Chancellor <nathan@...nel.org>
---
 drivers/gpu/drm/radeon/pptable.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/radeon/pptable.h b/drivers/gpu/drm/radeon/pptable.h
index b7f22597ee95..969a8fb0ee9e 100644
--- a/drivers/gpu/drm/radeon/pptable.h
+++ b/drivers/gpu/drm/radeon/pptable.h
@@ -439,7 +439,7 @@ typedef struct _StateArray{
     //how many states we have 
     UCHAR ucNumEntries;

-    ATOM_PPLIB_STATE_V2 states[] __counted_by(ucNumEntries);
+    ATOM_PPLIB_STATE_V2 states[] /* __counted_by(ucNumEntries) */;
 }StateArray;

---
base-commit: e64e8f7c178e5228e0b2dbb504b9dc75953a319f
change-id: 20240529-drop-counted-by-radeon-states-state-array-01936ded4c18

Best regards,
-- 
Nathan Chancellor <nathan@...nel.org>