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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-492690a1a85sm93653035e9.15.2026.06.25.23.48.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 25 Jun 2026 23:48:12 -0700 (PDT) Date: Fri, 26 Jun 2026 07:48:10 +0100 From: David Laight To: suryasaimadhu Cc: andy@kernel.org, gregkh@linuxfoundation.org, dri-devel@lists.freedesktop.org, linux-fbdev@vger.kernel.org, linux-staging@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: [PATCH] staging: fbtft: fix unaligned access and buffer size when startbyte is used Message-ID: <20260626074810.433c4006@pumpkin> In-Reply-To: <20260625103041.281190-1-suryasaimadhu369@gmail.com> References: <20260625103041.281190-1-suryasaimadhu369@gmail.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-fbdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Thu, 25 Jun 2026 18:30:41 +0800 suryasaimadhu wrote: > When par->startbyte is non-zero, buf is advanced by one byte creating > an unaligned pointer for 16-bit types (u16, __be16). Dereferencing this > unaligned pointer can cause a kernel panic on strict-alignment > architectures. > > Fix by using put_unaligned() instead of direct pointer dereference. > > Also fix incorrect buffer size calculation in fbtft_write_buf_dc() call: > len * (sizeof(data_type) + offset) /* wrong: multiplies offset by len */ > len * sizeof(data_type) + offset /* correct: one startbyte + > len items */ That should probably be a separate patch. > > Signed-off-by: suryasaimadhu > --- > drivers/staging/fbtft/fbtft-bus.c | 13 ++++++++----- > 1 file changed, 8 insertions(+), 5 deletions(-) > > diff --git a/drivers/staging/fbtft/fbtft-bus.c b/drivers/staging/fbtft/fbtft-bus.c > index 2169f8d1d..cfcf4d7e7 100644 > --- a/drivers/staging/fbtft/fbtft-bus.c > +++ b/drivers/staging/fbtft/fbtft-bus.c > @@ -4,6 +4,7 @@ > #include > #include > #include "fbtft.h" > +#include > > /***************************************************************************** > * > @@ -40,7 +41,7 @@ void func(struct fbtft_par *par, int len, ...) \ I'd consider changing that to: func(struct fbtft_par *par, int len, u8 cmd, ...) and probably reducing len by one. It makes it more obvious that the first parameter is mandatory and the ... is associated data. David > offset = 1; \ > } \ > \ > - *buf = modifier((data_type)va_arg(args, unsigned int)); \ > + put_unaligned(modifier((data_type)va_arg(args, unsigned int)), buf); \ > ret = fbtft_write_buf_dc(par, par->buf, sizeof(data_type) + offset, \ > 0); \ > if (ret < 0) \ > @@ -52,11 +53,13 @@ void func(struct fbtft_par *par, int len, ...) \ > \ > if (len) { \ > i = len; \ > - while (i--) \ > - *buf++ = modifier((data_type)va_arg(args, \ > - unsigned int)); \ > + while (i--) { \ > + put_unaligned(modifier((data_type)va_arg(args, \ > + unsigned int)), buf); \ > + buf++; \ > + } \ > fbtft_write_buf_dc(par, par->buf, \ > - len * (sizeof(data_type) + offset), 1); \ > + len * sizeof(data_type) + offset, 1); \ > } \ > out: \ > va_end(args); \