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[212.51.149.33]) by smtp.gmail.com with ESMTPSA id g25-20020a056402115900b004c4eed3fe20sm5552210edw.5.2023.04.17.01.42.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 17 Apr 2023 01:42:37 -0700 (PDT) Date: Mon, 17 Apr 2023 10:42:35 +0200 From: Daniel Vetter To: Thomas Zimmermann Cc: Sui Jingfeng <15330273260@189.cn>, Maxime Ripard , David Airlie , Daniel Vetter , Sui Jingfeng , Li Yi , Javier Martinez Canillas , Helge Deller , Lucas De Marchi , linux-kernel@vger.kernel.org, linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org, loongson-kernel@lists.loongnix.cn Subject: Re: [PATCH v2] drm/fbdev-generic: prohibit potential out-of-bounds access Message-ID: Mail-Followup-To: Thomas Zimmermann , Sui Jingfeng <15330273260@189.cn>, Maxime Ripard , David Airlie , Sui Jingfeng , Li Yi , Javier Martinez Canillas , Helge Deller , Lucas De Marchi , linux-kernel@vger.kernel.org, linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org, loongson-kernel@lists.loongnix.cn References: <20230413180622.1014016-1-15330273260@189.cn> <32a1510e-d38a-ffb6-8e8d-026f8b3aa17a@189.cn> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Operating-System: Linux phenom 6.1.0-7-amd64 Precedence: bulk List-ID: X-Mailing-List: linux-fbdev@vger.kernel.org On Mon, Apr 17, 2023 at 09:29:07AM +0200, Thomas Zimmermann wrote: > Hi > > Am 14.04.23 um 12:58 schrieb Sui Jingfeng: > > Hi, > > > > On 2023/4/14 03:16, Thomas Zimmermann wrote: > > > Hi, > > > > > > thanks for the patch. This is effectively a revert of commit > > > 8fbc9af55de0 ("drm/fbdev-generic: Set screen size to size of GEM > > > buffer"). Please add a Fixes tag. > > > > > > Am 13.04.23 um 20:06 schrieb Sui Jingfeng: > > > > From: Sui Jingfeng > > > > > > > > The crazy fbdev test of IGT may write after EOF, which lead to > > > > out-of-bound > > > > > > Please drop 'crazy'. :) > > > > This is OK. > > > > By using the world 'crazy', > > > > I meant that the test is very good and maybe it is written by > > professional  peoples > > > > with the guidance by  experienced  engineer. So that even the corner get > > tested. > > > > > > > > > > > access for the drm drivers using fbdev-generic. For example, run > > > > fbdev test > > > > on a x86-64+ast2400 platform with 1680x1050 resolution will > > > > cause the linux > > > > kernel hang with following call trace: > > > > > > > >    Oops: 0000 [#1] PREEMPT SMP PTI > > > >    [IGT] fbdev: starting subtest eof > > > >    Workqueue: events drm_fb_helper_damage_work [drm_kms_helper] > > > >    [IGT] fbdev: starting subtest nullptr > > > > > > > >    RIP: 0010:memcpy_erms+0xa/0x20 > > > >    RSP: 0018:ffffa17d40167d98 EFLAGS: 00010246 > > > >    RAX: ffffa17d4eb7fa80 RBX: ffffa17d40e0aa80 RCX: 00000000000014c0 > > > >    RDX: 0000000000001a40 RSI: ffffa17d40e0b000 RDI: ffffa17d4eb80000 > > > >    RBP: ffffa17d40167e20 R08: 0000000000000000 R09: ffff89522ecff8c0 > > > >    R10: ffffa17d4e4c5000 R11: 0000000000000000 R12: ffffa17d4eb7fa80 > > > >    R13: 0000000000001a40 R14: 000000000000041a R15: ffffa17d40167e30 > > > >    FS:  0000000000000000(0000) GS:ffff895257380000(0000) > > > > knlGS:0000000000000000 > > > >    CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > > >    CR2: ffffa17d40e0b000 CR3: 00000001eaeca006 CR4: 00000000001706e0 > > > >    Call Trace: > > > >     > > > >     ? drm_fbdev_generic_helper_fb_dirty+0x207/0x330 [drm_kms_helper] > > > >     drm_fb_helper_damage_work+0x8f/0x170 [drm_kms_helper] > > > >     process_one_work+0x21f/0x430 > > > >     worker_thread+0x4e/0x3c0 > > > >     ? __pfx_worker_thread+0x10/0x10 > > > >     kthread+0xf4/0x120 > > > >     ? __pfx_kthread+0x10/0x10 > > > >     ret_from_fork+0x2c/0x50 > > > >     > > > >    CR2: ffffa17d40e0b000 > > > >    ---[ end trace 0000000000000000 ]--- > > > > > > > > The indirect reason is drm_fb_helper_memory_range_to_clip() > > > > generate damage > > > > rectangles which partially or completely go out of the active > > > > display area. > > > > The second of argument 'off' is passing from the user-space, > > > > this will lead > > > > to the out-of-bound if it is large than (fb_height + 1) * > > > > fb_pitches; while > > > > DIV_ROUND_UP() may also controbute to error by 1. > > > > > > > > This patch will add code to restrict the damage rect computed go > > > > beyond of > > > > the last line of the framebuffer. > > > > > > > > Signed-off-by: Sui Jingfeng > > > > --- > > > >   drivers/gpu/drm/drm_fb_helper.c     | 16 ++++++++++++---- > > > >   drivers/gpu/drm/drm_fbdev_generic.c |  2 +- > > > >   2 files changed, 13 insertions(+), 5 deletions(-) > > > > > > > > diff --git a/drivers/gpu/drm/drm_fb_helper.c > > > > b/drivers/gpu/drm/drm_fb_helper.c > > > > index 64458982be40..6bb1b8b27d7a 100644 > > > > --- a/drivers/gpu/drm/drm_fb_helper.c > > > > +++ b/drivers/gpu/drm/drm_fb_helper.c > > > > @@ -641,19 +641,27 @@ static void drm_fb_helper_damage(struct > > > > drm_fb_helper *helper, u32 x, u32 y, > > > >   static void drm_fb_helper_memory_range_to_clip(struct fb_info > > > > *info, off_t off, size_t len, > > > >                              struct drm_rect *clip) > > > >   { > > > > +    u32 line_length = info->fix.line_length; > > > > +    u32 fb_height = info->var.yres; > > > >       off_t end = off + len; > > > >       u32 x1 = 0; > > > > -    u32 y1 = off / info->fix.line_length; > > > > +    u32 y1 = off / line_length; > > > >       u32 x2 = info->var.xres; > > > > -    u32 y2 = DIV_ROUND_UP(end, info->fix.line_length); > > > > +    u32 y2 = DIV_ROUND_UP(end, line_length); > > > > + > > > > +    /* Don't allow any of them beyond the bottom bound of > > > > display area */ > > > > +    if (y1 > fb_height) > > > > +        y1 = fb_height; > > > > +    if (y2 > fb_height) > > > > +        y2 = fb_height; > > > >         if ((y2 - y1) == 1) { > > > >           /* > > > >            * We've only written to a single scanline. Try to reduce > > > >            * the number of horizontal pixels that need an update. > > > >            */ > > > > -        off_t bit_off = (off % info->fix.line_length) * 8; > > > > -        off_t bit_end = (end % info->fix.line_length) * 8; > > > > +        off_t bit_off = (off % line_length) * 8; > > > > +        off_t bit_end = (end % line_length) * 8; > > > > > > Please scratch all these changes. The current code should work as > > > intended. Only the generic fbdev emulation uses this code and it > > > should really be moved there at some point. > > > > > > Are you meant  that we should remove all these changes in > > drivers/gpu/drm/drm_fb_helper.c ? > > As Daniel mentioned, there's the discussion in the other thread. I don't > want to reopen it here. Just to summarize: I'm not convinced that this > should be DRM code because it can be shared with other fbdev drivers. > > [...] > > > > > diff --git a/drivers/gpu/drm/drm_fbdev_generic.c > > > > b/drivers/gpu/drm/drm_fbdev_generic.c > > > > index 8e5148bf40bb..b057cfbba938 100644 > > > > --- a/drivers/gpu/drm/drm_fbdev_generic.c > > > > +++ b/drivers/gpu/drm/drm_fbdev_generic.c > > > > @@ -94,7 +94,7 @@ static int > > > > drm_fbdev_generic_helper_fb_probe(struct drm_fb_helper > > > > *fb_helper, > > > >       fb_helper->buffer = buffer; > > > >       fb_helper->fb = buffer->fb; > > > >   -    screen_size = buffer->gem->size; > > > > +    screen_size = sizes->surface_height * buffer->fb->pitches[0]; > > This has been bothering me over the weekend. And I think it's because what > we want the screen_size to be heigth * pitch, but the mmap'ed memory is > still at page granularity. Therefore... > > [...] > > > > > > >       screen_buffer = vzalloc(screen_size); > > ... this line should explicitly allocate multiples of pages. Something like > > /* allocate page-size multiples for mmap */ > vzalloc(PAGE_ALIGN(screen_size)) > > It has not been a bug so far because vzalloc() always returns full pages > IIRC. It's still worth fixing. So gem_bo are supposed to be at least PAGE_SIZE aligned. So maybe we just put a comment in here why this assumption holds, and reinforce it with a WARN_ON? I think that would address the concerns here? But I concur with Sui that this is a separate issue which should be sorted out in a separate patch. -Daniel > > Best regards > Thomas > > > > > >       if (!screen_buffer) { > > > >           ret = -ENOMEM; > > > > > -- > Thomas Zimmermann > Graphics Driver Developer > SUSE Software Solutions Germany GmbH > Maxfeldstr. 5, 90409 Nürnberg, Germany > (HRB 36809, AG Nürnberg) > Geschäftsführer: Ivo Totev -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch