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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id p62sm9602982pfb.93.2020.05.18.15.56.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 18 May 2020 15:56:52 -0700 (PDT) Date: Mon, 18 May 2020 15:56:51 -0700 From: Kees Cook To: "Gustavo A. R. Silva" Subject: Re: [PATCH] soc: fsl: qe: Replace one-element array and use struct_size() helper Message-ID: <202005181529.C0CB448FBB@keescook> References: <20200518221904.GA22274@embeddedor> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200518221904.GA22274@embeddedor> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200518_155655_048962_D0F24C2F X-CRM114-Status: GOOD ( 27.86 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "Gustavo A. R. Silva" , linux-kernel@vger.kernel.org, Li Yang , linuxppc-dev@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org, Qiang Zhao Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, May 18, 2020 at 05:19:04PM -0500, Gustavo A. R. Silva wrote: > The current codebase makes use of one-element arrays in the following > form: > > struct something { > int length; > u8 data[1]; > }; > > struct something *instance; > > instance = kmalloc(sizeof(*instance) + size, GFP_KERNEL); > instance->length = size; > memcpy(instance->data, source, size); > > but the preferred mechanism to declare variable-length types such as > these ones is a flexible array member[1][2], introduced in C99: > > struct foo { > int stuff; > struct boo array[]; > }; > > By making use of the mechanism above, we will get a compiler warning > in case the flexible array does not occur last in the structure, which > will help us prevent some kind of undefined behavior bugs from being > inadvertently introduced[3] to the codebase from now on. So, replace > the one-element array with a flexible-array member. > > Also, make use of the new struct_size() helper to properly calculate the > size of struct qe_firmware. > > This issue was found with the help of Coccinelle and, audited and fixed > _manually_. > > [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html > [2] https://github.com/KSPP/linux/issues/21 > [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") > > Signed-off-by: Gustavo A. R. Silva > --- > drivers/soc/fsl/qe/qe.c | 4 ++-- > include/soc/fsl/qe/qe.h | 2 +- > 2 files changed, 3 insertions(+), 3 deletions(-) > > diff --git a/drivers/soc/fsl/qe/qe.c b/drivers/soc/fsl/qe/qe.c > index 447146861c2c1..2df20d6f85fa4 100644 > --- a/drivers/soc/fsl/qe/qe.c > +++ b/drivers/soc/fsl/qe/qe.c > @@ -448,7 +448,7 @@ int qe_upload_firmware(const struct qe_firmware *firmware) > unsigned int i; > unsigned int j; > u32 crc; > - size_t calc_size = sizeof(struct qe_firmware); > + size_t calc_size; > size_t length; > const struct qe_header *hdr; > > @@ -480,7 +480,7 @@ int qe_upload_firmware(const struct qe_firmware *firmware) > } > > /* Validate the length and check if there's a CRC */ > - calc_size += (firmware->count - 1) * sizeof(struct qe_microcode); > + calc_size = struct_size(firmware, microcode, firmware->count); > > for (i = 0; i < firmware->count; i++) > /* > diff --git a/include/soc/fsl/qe/qe.h b/include/soc/fsl/qe/qe.h > index e282ac01ec081..3feddfec9f87d 100644 > --- a/include/soc/fsl/qe/qe.h > +++ b/include/soc/fsl/qe/qe.h > @@ -307,7 +307,7 @@ struct qe_firmware { > u8 revision; /* The microcode version revision */ > u8 padding; /* Reserved, for alignment */ > u8 reserved[4]; /* Reserved, for future expansion */ > - } __attribute__ ((packed)) microcode[1]; > + } __packed microcode[]; > /* All microcode binaries should be located here */ > /* CRC32 should be located here, after the microcode binaries */ > } __attribute__ ((packed)); > -- > 2.26.2 > Hm, looking at this code, I see a few other things that need to be fixed: 1) drivers/tty/serial/ucc_uart.c does not do a be32_to_cpu() conversion on the length test (understandably, a little-endian system has never run this code since it's ppc specific), but it's still wrong: if (firmware->header.length != fw->size) { compare to the firmware loader: length = be32_to_cpu(hdr->length); 2) drivers/soc/fsl/qe/qe.c does not perform bounds checking on the per-microcode offsets, so the uploader might send data outside the firmware buffer. Perhaps: diff --git a/drivers/soc/fsl/qe/qe.c b/drivers/soc/fsl/qe/qe.c index 447146861c2c..c4e0bc452f03 100644 --- a/drivers/soc/fsl/qe/qe.c +++ b/drivers/soc/fsl/qe/qe.c @@ -451,6 +451,7 @@ int qe_upload_firmware(const struct qe_firmware *firmware) size_t calc_size = sizeof(struct qe_firmware); size_t length; const struct qe_header *hdr; + void *firmware_end; if (!firmware) { printk(KERN_ERR "qe-firmware: invalid pointer\n"); @@ -491,19 +492,39 @@ int qe_upload_firmware(const struct qe_firmware *firmware) calc_size += sizeof(__be32) * be32_to_cpu(firmware->microcode[i].count); - /* Validate the length */ + /* Validate total length */ if (length != calc_size + sizeof(__be32)) { printk(KERN_ERR "qe-firmware: invalid length\n"); return -EPERM; } /* Validate the CRC */ - crc = be32_to_cpu(*(__be32 *)((void *)firmware + calc_size)); + firmware_end = (void *)firmware + calc_size; + crc = be32_to_cpu(*(__be32 *)firmware_end); if (crc != crc32(0, firmware, calc_size)) { printk(KERN_ERR "qe-firmware: firmware CRC is invalid\n"); return -EIO; } + /* Validate ucode lengths and offsets */ + for (i = 0; i < firmware->count; i++) { + const struct qe_microcode *ucode = &firmware->microcode[i]; + __be32 *code; + size_t count; + + if (!ucode->code_offset) + continue; + + code = (void *)firmware + be32_to_cpu(ucode->code_offset); + count = be32_to_cpu(ucode->count) * sizeof(*code); + + if (code < firmware || code >= firmware_end || + code + count < firmware || code + count >= firmware_end) { + printk(KERN_ERR "qe-firmware: invalid ucode offset\n"); + return -EIO; + } + } + /* * If the microcode calls for it, split the I-RAM. */ I haven't tested this. -- Kees Cook _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel