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[47.55.120.4]) by smtp.gmail.com with ESMTPSA id af79cd13be357-8b3295db543sm457101985a.38.2025.11.21.15.51.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 21 Nov 2025 15:51:54 -0800 (PST) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1vMauv-00000001bzu-1Ue0; Fri, 21 Nov 2025 19:51:53 -0400 Date: Fri, 21 Nov 2025 19:51:53 -0400 From: Jason Gunthorpe To: Nirbhay Sharma Cc: Kevin Tian , Shuah Khan , iommu@lists.linux.dev, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, david.hunter.linux@gmail.com, linux-kernel-mentees@lists.linuxfoundation.org Subject: Re: [PATCH] selftests/iommu: Fix array-bounds warning in get_hw_info Message-ID: <20251121235153.GK233636@ziepe.ca> References: <20251113200854.429515-2-nirbhay.lkd@gmail.com> Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251113200854.429515-2-nirbhay.lkd@gmail.com> On Fri, Nov 14, 2025 at 01:38:55AM +0530, Nirbhay Sharma wrote: > GCC warns about potential out-of-bounds access when the test provides > a buffer smaller than struct iommu_test_hw_info: > > iommufd_utils.h:817:37: warning: array subscript 'struct > iommu_test_hw_info[0]' is partly outside array bounds of 'struct > iommu_test_hw_info_buffer_smaller[1]' > [-Warray-bounds=] > 817 | assert(!info->flags); > | ~~~~^~~~~~~ > > The warning occurs because 'info' is cast to a pointer to the full > 8-byte struct at the top of the function, but the buffer_smaller test > case passes only a 4-byte buffer. While the code correctly checks > data_len before accessing each field, GCC's flow analysis with inlining > doesn't recognize that the size check protects the access. > > Fix this by accessing fields through appropriately-typed pointers that > match the actual field sizes (__u32), declared only after the bounds > check. This makes the relationship between the size check and memory > access explicit to the compiler. > > Signed-off-by: Nirbhay Sharma > --- > tools/testing/selftests/iommu/iommufd_utils.h | 19 +++++++++++++------ > 1 file changed, 13 insertions(+), 6 deletions(-) > > diff --git a/tools/testing/selftests/iommu/iommufd_utils.h b/tools/testing/selftests/iommu/iommufd_utils.h > index 9f472c20c190..37c1b994008c 100644 > --- a/tools/testing/selftests/iommu/iommufd_utils.h > +++ b/tools/testing/selftests/iommu/iommufd_utils.h > @@ -770,7 +770,6 @@ static int _test_cmd_get_hw_info(int fd, __u32 device_id, __u32 data_type, > void *data, size_t data_len, > uint32_t *capabilities, uint8_t *max_pasid) > { > - struct iommu_test_hw_info *info = (struct iommu_test_hw_info *)data; > struct iommu_hw_info cmd = { > .size = sizeof(cmd), > .dev_id = device_id, > @@ -810,11 +809,19 @@ static int _test_cmd_get_hw_info(int fd, __u32 device_id, __u32 data_type, > } > } > > - if (info) { > - if (data_len >= offsetofend(struct iommu_test_hw_info, test_reg)) > - assert(info->test_reg == IOMMU_HW_INFO_SELFTEST_REGVAL); > - if (data_len >= offsetofend(struct iommu_test_hw_info, flags)) > - assert(!info->flags); > + if (data) { > + if (data_len >= offsetofend(struct iommu_test_hw_info, > + test_reg)) { > + __u32 *test_reg = (__u32 *)data + 1; This seems too obfuscated, can't we keep the struct somehow and still remove the warning? I also feel like you have a compiler bug here, if gcc has inlined enough to know the size of data then it surely should know the constant value of data_len? Failing that, how about just change the caller, maybe like this: --- a/tools/testing/selftests/iommu/iommufd.c +++ b/tools/testing/selftests/iommu/iommufd.c @@ -760,6 +760,7 @@ TEST_F(iommufd_ioas, get_hw_info) } buffer_larger; struct iommu_test_hw_info_buffer_smaller { __u32 flags; + struct iommu_test_hw_info dummy; } buffer_smaller; if (self->device_id) { @@ -791,9 +792,11 @@ TEST_F(iommufd_ioas, get_hw_info) * Provide a user_buffer with size smaller than the exact size to check if * the fields within the size range still gets updated. */ - test_cmd_get_hw_info(self->device_id, - IOMMU_HW_INFO_TYPE_DEFAULT, - &buffer_smaller, sizeof(buffer_smaller)); + test_cmd_get_hw_info( + self->device_id, IOMMU_HW_INFO_TYPE_DEFAULT, + &buffer_smaller, + offsetofend(struct iommu_test_hw_info_buffer_smaller, + flags)); test_cmd_get_hw_info_pasid(self->device_id, &max_pasid); ASSERT_EQ(0, max_pasid); if (variant->pasid_capable) { Jason