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    Subject[PATCH 5.4 306/475] video: fbdev: sm712fb: Fix crash in smtcfb_write()
    Date
    From: Zheyu Ma <zheyuma97@gmail.com>

    [ Upstream commit 4f01d09b2bbfbcb47b3eb305560a7f4857a32260 ]

    When the sm712fb driver writes three bytes to the framebuffer, the
    driver will crash:

    BUG: unable to handle page fault for address: ffffc90001ffffff
    RIP: 0010:smtcfb_write+0x454/0x5b0
    Call Trace:
    vfs_write+0x291/0xd60
    ? do_sys_openat2+0x27d/0x350
    ? __fget_light+0x54/0x340
    ksys_write+0xce/0x190
    do_syscall_64+0x43/0x90
    entry_SYSCALL_64_after_hwframe+0x44/0xae

    Fix it by removing the open-coded endianness fixup-code.

    Signed-off-by: Zheyu Ma <zheyuma97@gmail.com>
    Signed-off-by: Helge Deller <deller@gmx.de>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/video/fbdev/sm712fb.c | 21 ++++-----------------
    1 file changed, 4 insertions(+), 17 deletions(-)

    --- a/drivers/video/fbdev/sm712fb.c
    +++ b/drivers/video/fbdev/sm712fb.c
    @@ -1119,7 +1119,7 @@ static ssize_t smtcfb_write(struct fb_in
    count = total_size - p;
    }

    - buffer = kmalloc((count > PAGE_SIZE) ? PAGE_SIZE : count, GFP_KERNEL);
    + buffer = kmalloc(PAGE_SIZE, GFP_KERNEL);
    if (!buffer)
    return -ENOMEM;

    @@ -1137,24 +1137,11 @@ static ssize_t smtcfb_write(struct fb_in
    break;
    }

    - for (i = c >> 2; i--;) {
    - fb_writel(big_swap(*src), dst++);
    + for (i = (c + 3) >> 2; i--;) {
    + fb_writel(big_swap(*src), dst);
    + dst++;
    src++;
    }
    - if (c & 3) {
    - u8 *src8 = (u8 *)src;
    - u8 __iomem *dst8 = (u8 __iomem *)dst;
    -
    - for (i = c & 3; i--;) {
    - if (i & 1) {
    - fb_writeb(*src8++, ++dst8);
    - } else {
    - fb_writeb(*src8++, --dst8);
    - dst8 += 2;
    - }
    - }
    - dst = (u32 __iomem *)dst8;
    - }

    *ppos += c;
    buf += c;

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