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[81.40.121.121]) by smtp.gmail.com with ESMTPSA id o2sm10352365wrj.21.2020.08.22.05.31.30 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 22 Aug 2020 05:31:31 -0700 (PDT) Subject: Re: [PATCH] ati-vga: Fix checks in ati_2d_blt() to avoid crash To: BALATON Zoltan , qemu-devel@nongnu.org References: <20200406204029.19559747D5D@zero.eik.bme.hu> From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= Autocrypt: addr=philmd@redhat.com; keydata= mQINBDXML8YBEADXCtUkDBKQvNsQA7sDpw6YLE/1tKHwm24A1au9Hfy/OFmkpzo+MD+dYc+7 bvnqWAeGweq2SDq8zbzFZ1gJBd6+e5v1a/UrTxvwBk51yEkadrpRbi+r2bDpTJwXc/uEtYAB GvsTZMtiQVA4kRID1KCdgLa3zztPLCj5H1VZhqZsiGvXa/nMIlhvacRXdbgllPPJ72cLUkXf z1Zu4AkEKpccZaJspmLWGSzGu6UTZ7UfVeR2Hcc2KI9oZB1qthmZ1+PZyGZ/Dy+z+zklC0xl XIpQPmnfy9+/1hj1LzJ+pe3HzEodtlVA+rdttSvA6nmHKIt8Ul6b/h1DFTmUT1lN1WbAGxmg CH1O26cz5nTrzdjoqC/b8PpZiT0kO5MKKgiu5S4PRIxW2+RA4H9nq7nztNZ1Y39bDpzwE5Sp bDHzd5owmLxMLZAINtCtQuRbSOcMjZlg4zohA9TQP9krGIk+qTR+H4CV22sWldSkVtsoTaA2 qNeSJhfHQY0TyQvFbqRsSNIe2gTDzzEQ8itsmdHHE/yzhcCVvlUzXhAT6pIN0OT+cdsTTfif MIcDboys92auTuJ7U+4jWF1+WUaJ8gDL69ThAsu7mGDBbm80P3vvUZ4fQM14NkxOnuGRrJxO qjWNJ2ZUxgyHAh5TCxMLKWZoL5hpnvx3dF3Ti9HW2dsUUWICSQARAQABtDJQaGlsaXBwZSBN YXRoaWV1LURhdWTDqSAoUGhpbCkgPHBoaWxtZEByZWRoYXQuY29tPokCVQQTAQgAPwIbDwYL CQgHAwIGFQgCCQoLBBYCAwECHgECF4AWIQSJweePYB7obIZ0lcuio/1u3q3A3gUCXsfWwAUJ KtymWgAKCRCio/1u3q3A3ircD/9Vjh3aFNJ3uF3hddeoFg1H038wZr/xi8/rX27M1Vj2j9VH 0B8Olp4KUQw/hyO6kUxqkoojmzRpmzvlpZ0cUiZJo2bQIWnvScyHxFCv33kHe+YEIqoJlaQc JfKYlbCoubz+02E2A6bFD9+BvCY0LBbEj5POwyKGiDMjHKCGuzSuDRbCn0Mz4kCa7nFMF5Jv piC+JemRdiBd6102ThqgIsyGEBXuf1sy0QIVyXgaqr9O2b/0VoXpQId7yY7OJuYYxs7kQoXI 6WzSMpmuXGkmfxOgbc/L6YbzB0JOriX0iRClxu4dEUg8Bs2pNnr6huY2Ft+qb41RzCJvvMyu gS32LfN0bTZ6Qm2A8ayMtUQgnwZDSO23OKgQWZVglGliY3ezHZ6lVwC24Vjkmq/2yBSLakZE 6DZUjZzCW1nvtRK05ebyK6tofRsx8xB8pL/kcBb9nCuh70aLR+5cmE41X4O+MVJbwfP5s/RW 9BFSL3qgXuXso/3XuWTQjJJGgKhB6xXjMmb1J4q/h5IuVV4juv1Fem9sfmyrh+Wi5V1IzKI7 RPJ3KVb937eBgSENk53P0gUorwzUcO+ASEo3Z1cBKkJSPigDbeEjVfXQMzNt0oDRzpQqH2vp apo2jHnidWt8BsckuWZpxcZ9+/9obQ55DyVQHGiTN39hkETy3Emdnz1JVHTU0Q== Message-ID: <2041026f-7a88-d8f7-8738-968e1394e8c6@redhat.com> Date: Sat, 22 Aug 2020 14:31:29 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: <20200406204029.19559747D5D@zero.eik.bme.hu> Content-Language: en-US Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=philmd@redhat.com X-Mimecast-Spam-Score: 0.002 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=207.211.31.81; envelope-from=philmd@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/08/22 08:31:35 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -40 X-Spam_score: -4.1 X-Spam_bar: ---- X-Spam_report: (-4.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Peter Maydell , Mauro Matteo Cascella , Michael Tokarev , Gerd Hoffmann , Prasad J Pandit Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 4/6/20 10:34 PM, BALATON Zoltan wrote: > In some corner cases (that never happen during normal operation but a > malicious guest could program wrong values) pixman functions were > called with parameters that result in a crash. Fix this and add more > checks to disallow such cases. (Fair) question on IRC. Is this patch fixing CVE-2020-24352? Public on August 14, 2020 Description An out-of-bounds memory access flaw was found in the ATI VGA device implementation of the QEMU emulator. This flaw occurs in the ati_2d_blt() routine while handling MMIO write operations through the ati_mm_write() callback. A malicious guest could use this flaw to crash the QEMU process on the host, resulting in a denial of service. This points to a BZ#1847385 which is private: "You are not authorized to access bug #1847385. Most likely the bug has been restricted for internal development processes and we cannot grant access." https://bugzilla.redhat.com/show_bug.cgi?id=1847385 Maybe we could improve the security process, when a CVE embargo expires, the public statement could point at the commit(s) fixing the bug. > > Reported-by: Ziming Zhang I'm not sure this is the correct CVE because CVE-2020-24352 is said reported by Yi Ren from the Alibaba Cloud Intelligence Security Team. Thanks, Phil. > Signed-off-by: BALATON Zoltan > --- > hw/display/ati_2d.c | 37 ++++++++++++++++++++++++++----------- > 1 file changed, 26 insertions(+), 11 deletions(-) > > diff --git a/hw/display/ati_2d.c b/hw/display/ati_2d.c > index 42e82311eb..23a8ae0cd8 100644 > --- a/hw/display/ati_2d.c > +++ b/hw/display/ati_2d.c > @@ -53,12 +53,20 @@ void ati_2d_blt(ATIVGAState *s) > s->vga.vbe_start_addr, surface_data(ds), surface_stride(ds), > surface_bits_per_pixel(ds), > (s->regs.dp_mix & GMC_ROP3_MASK) >> 16); > - int dst_x = (s->regs.dp_cntl & DST_X_LEFT_TO_RIGHT ? > - s->regs.dst_x : s->regs.dst_x + 1 - s->regs.dst_width); > - int dst_y = (s->regs.dp_cntl & DST_Y_TOP_TO_BOTTOM ? > - s->regs.dst_y : s->regs.dst_y + 1 - s->regs.dst_height); > + unsigned dst_x = (s->regs.dp_cntl & DST_X_LEFT_TO_RIGHT ? > + s->regs.dst_x : s->regs.dst_x + 1 - s->regs.dst_width); > + unsigned dst_y = (s->regs.dp_cntl & DST_Y_TOP_TO_BOTTOM ? > + s->regs.dst_y : s->regs.dst_y + 1 - s->regs.dst_height); > int bpp = ati_bpp_from_datatype(s); > + if (!bpp) { > + qemu_log_mask(LOG_GUEST_ERROR, "Invalid bpp\n"); > + return; > + } > int dst_stride = DEFAULT_CNTL ? s->regs.dst_pitch : s->regs.default_pitch; > + if (!dst_stride) { > + qemu_log_mask(LOG_GUEST_ERROR, "Zero dest pitch\n"); > + return; > + } > uint8_t *dst_bits = s->vga.vram_ptr + (DEFAULT_CNTL ? > s->regs.dst_offset : s->regs.default_offset); > > @@ -82,12 +90,16 @@ void ati_2d_blt(ATIVGAState *s) > switch (s->regs.dp_mix & GMC_ROP3_MASK) { > case ROP3_SRCCOPY: > { > - int src_x = (s->regs.dp_cntl & DST_X_LEFT_TO_RIGHT ? > - s->regs.src_x : s->regs.src_x + 1 - s->regs.dst_width); > - int src_y = (s->regs.dp_cntl & DST_Y_TOP_TO_BOTTOM ? > - s->regs.src_y : s->regs.src_y + 1 - s->regs.dst_height); > + unsigned src_x = (s->regs.dp_cntl & DST_X_LEFT_TO_RIGHT ? > + s->regs.src_x : s->regs.src_x + 1 - s->regs.dst_width); > + unsigned src_y = (s->regs.dp_cntl & DST_Y_TOP_TO_BOTTOM ? > + s->regs.src_y : s->regs.src_y + 1 - s->regs.dst_height); > int src_stride = DEFAULT_CNTL ? > s->regs.src_pitch : s->regs.default_pitch; > + if (!src_stride) { > + qemu_log_mask(LOG_GUEST_ERROR, "Zero source pitch\n"); > + return; > + } > uint8_t *src_bits = s->vga.vram_ptr + (DEFAULT_CNTL ? > s->regs.src_offset : s->regs.default_offset); > > @@ -137,8 +149,10 @@ void ati_2d_blt(ATIVGAState *s) > dst_y * surface_stride(ds), > s->regs.dst_height * surface_stride(ds)); > } > - s->regs.dst_x += s->regs.dst_width; > - s->regs.dst_y += s->regs.dst_height; > + s->regs.dst_x = (s->regs.dp_cntl & DST_X_LEFT_TO_RIGHT ? > + dst_x + s->regs.dst_width : dst_x); > + s->regs.dst_y = (s->regs.dp_cntl & DST_Y_TOP_TO_BOTTOM ? > + dst_y + s->regs.dst_height : dst_y); > break; > } > case ROP3_PATCOPY: > @@ -179,7 +193,8 @@ void ati_2d_blt(ATIVGAState *s) > dst_y * surface_stride(ds), > s->regs.dst_height * surface_stride(ds)); > } > - s->regs.dst_y += s->regs.dst_height; > + s->regs.dst_y = (s->regs.dp_cntl & DST_Y_TOP_TO_BOTTOM ? > + dst_y + s->regs.dst_height : dst_y); > break; > } > default: >