From a7620cd6f659dfa685a445536a240182225a778c Mon Sep 17 00:00:00 2001 From: Abyss Watcher Date: Fri, 15 Nov 2024 17:09:21 +0100 Subject: [PATCH] linux fbdev subsystem api plugin --- .../framework/plugins/linux/graphics/fbdev.py | 314 ++++++++++++++++++ 1 file changed, 314 insertions(+) create mode 100644 volatility3/framework/plugins/linux/graphics/fbdev.py diff --git a/volatility3/framework/plugins/linux/graphics/fbdev.py b/volatility3/framework/plugins/linux/graphics/fbdev.py new file mode 100644 index 000000000..4bde6f62f --- /dev/null +++ b/volatility3/framework/plugins/linux/graphics/fbdev.py @@ -0,0 +1,314 @@ +# This file is Copyright 2024 Volatility Foundation and licensed under the Volatility Software License 1.0 +# which is available at https://www.volatilityfoundation.org/license/vsl-v1.0 +# +import logging +import io + +# Image manipulation functions are kept in the plugin, +# to prevent a general exit on missing PIL (pillow) dependency. +from PIL import Image +from dataclasses import dataclass +from typing import Type, List, Dict, Tuple +from volatility3.framework import constants, exceptions, interfaces +from volatility3.framework.configuration import requirements +from volatility3.framework.renderers import format_hints, TreeGrid, NotAvailableValue +from volatility3.framework.objects import utility +from volatility3.framework.constants import architectures +from volatility3.framework.symbols import linux + +vollog = logging.getLogger(__name__) + + +@dataclass +class Framebuffer: + """Framebuffer object internal representation. This is useful to unify an framebuffer with precalculated + properties and pass it through functions conveniently.""" + + id: str + xres_virtual: int + yres_virtual: int + line_length: int + bpp: int + """Bits Per Pixel""" + size: int + color_fields: Dict[str, Tuple[int, int, int]] + fb_info: interfaces.objects.ObjectInterface + + +class Fbdev(interfaces.plugins.PluginInterface): + """Extract framebuffers from the fbdev graphics subsystem""" + + _version = (1, 0, 0) + _required_framework_version = (2, 11, 0) + + @classmethod + def get_requirements(cls) -> List[interfaces.configuration.RequirementInterface]: + return [ + requirements.ModuleRequirement( + name="kernel", + description="Linux kernel", + architectures=architectures.LINUX_ARCHS, + ), + requirements.BooleanRequirement( + name="dump", + description="Dump framebuffers", + default=False, + optional=True, + ), + ] + + @classmethod + def parse_fb_pixel_bitfields( + cls, fb_var_screeninfo: interfaces.objects.ObjectInterface + ) -> Dict[str, Tuple[int, int, int]]: + """Organize a framebuffer pixel format into a dictionary. + This is needed to know the position and bitlength of a color inside + a pixel. + + Args: + fb_var_screeninfo: a fb_var_screeninfo kernel object instance + + Returns: + The color fields mappings + + Documentation: + include/uapi/linux/fb.h: + struct fb_bitfield { + __u32 offset; /* beginning of bitfield */ + __u32 length; /* length of bitfield */ + __u32 msb_right; /* != 0 : Most significant bit is right */ + }; + """ + # Naturally order by RGBA + color_mappings = [ + ("R", fb_var_screeninfo.red), + ("G", fb_var_screeninfo.green), + ("B", fb_var_screeninfo.blue), + ("A", fb_var_screeninfo.transp), + ] + color_fields = {} + for color_code, fb_bitfield in color_mappings: + color_fields[color_code] = ( + int(fb_bitfield.offset), + int(fb_bitfield.length), + int(fb_bitfield.msb_right), + ) + return color_fields + + @classmethod + def convert_fb_raw_buffer_to_image( + cls, + context: interfaces.context.ContextInterface, + kernel_name: str, + fb: Framebuffer, + ) -> Image.Image: + """Convert raw framebuffer pixels to an image. + + Args: + fb: the relevant Framebuffer object + + Returns: + A PIL Image object + + Documentation: + include/uapi/linux/fb.h: + /* Interpretation of offset for color fields: All offsets are from the right, + * inside a "pixel" value, which is exactly 'bits_per_pixel' wide (means: you + * can use the offset as right argument to <<). A pixel afterwards is a bit + * stream and is written to video memory as that unmodified. + """ + kernel = context.modules[kernel_name] + kernel_layer = context.layers[kernel.layer_name] + + raw_pixels = io.BytesIO(kernel_layer.read(fb.fb_info.screen_base, fb.size)) + bytes_per_pixel = fb.bpp // 8 + image = Image.new("RGBA", (fb.xres_virtual, fb.yres_virtual)) + + # This is not designed to be extremely fast (numpy isn't available), + # but convenient and dynamic for any color field layout. + for y in range(fb.yres_virtual): + for x in range(fb.xres_virtual): + raw_pixel = int.from_bytes(raw_pixels.read(bytes_per_pixel), "little") + pixel = [0, 0, 0, 255] + # The framebuffer is expected to have been correctly constructed, + # especially by parse_fb_pixel_bitfields, to get the needed RGBA mappings. + for i, color_code in enumerate(["R", "G", "B", "A"]): + offset, length, msb_right = fb.color_fields[color_code] + if length == 0: + continue + color_value = (raw_pixel >> offset) & (2**length - 1) + if msb_right: + # Reverse bit order + color_value = int( + "{:0{length}b}".format(color_value, length=length)[::-1], 2 + ) + pixel[i] = color_value + image.putpixel((x, y), tuple(pixel)) + + return image + + @classmethod + def dump_fb( + cls, + context: interfaces.context.ContextInterface, + kernel_name: str, + open_method: Type[interfaces.plugins.FileHandlerInterface], + fb: Framebuffer, + convert_to_image: bool, + image_format: str = "PNG", + ) -> str: + """Dump a Framebuffer raw buffer to disk. + + Args: + fb: the relevant Framebuffer object + convert_to_image: a boolean specifying if the buffer should be converted to an image + image_format: the target PIL image format (defaults to PNG) + + Returns: + The filename of the dumped buffer. + """ + kernel = context.modules[kernel_name] + kernel_layer = context.layers[kernel.layer_name] + base_filename = f"{fb.id}_{fb.xres_virtual}x{fb.yres_virtual}_{fb.bpp}bpp" + if convert_to_image: + image = cls.convert_fb_raw_buffer_to_image(context, kernel_name, fb) + output = io.BytesIO() + image.save(output, image_format) + file_handle = open_method(f"{base_filename}.{image_format.lower()}") + file_handle.write(output.getvalue()) + else: + raw_pixels = kernel_layer.read(fb.fb_info.screen_base, fb.size) + file_handle = open_method(f"{base_filename}.raw") + file_handle.write(raw_pixels) + + file_handle.close() + return file_handle.preferred_filename + + @classmethod + def parse_fb_info( + cls, + fb_info: interfaces.objects.ObjectInterface, + ) -> Framebuffer: + """Parse an fb_info struct + Args: + fb_info: an fb_info kernel object live instance + + Returns: + A Framebuffer object + + Documentation: + https://docs.kernel.org/fb/api.html: + - struct fb_fix_screeninfo stores device independent unchangeable information about the frame buffer device and the current format. + Those information can't be directly modified by applications, but can be changed by the driver when an application modifies the format. + - struct fb_var_screeninfo stores device independent changeable information about a frame buffer device, its current format and video mode, + as well as other miscellaneous parameters. + """ + # NotAvailableValue() messes with the filename output on disk + id = utility.array_to_string(fb_info.fix.id) or "N-A" + color_fields = None + + # 0 = color, 1 = grayscale, >1 = FOURCC + if fb_info.var.grayscale in [0, 1]: + color_fields = cls.parse_fb_pixel_bitfields(fb_info.var) + + # There a lot of tricky pixel formats used by drivers and vendors in include/uapi/linux/videodev2.h. + # As Volatility3 is not a video format converter, it is best to play it safe and let the user parse + # the raw data manually (with ffmpeg for example). + elif fb_info.var.grayscale > 1: + fourcc = linux.LinuxUtilities.convert_fourcc_code(fb_info.var.grayscale) + warn_msg = f"""Framebuffer "{id}" uses a FOURCC pixel format "{fourcc}" that isn't natively supported. +You can try using ffmpeg to decode the raw buffer. Example usage: +"ffmpeg -pix_fmts" to list supported formats, then +"ffmpeg -f rawvideo -video_size {fb_info.var.xres_virtual}x{fb_info.var.yres_virtual} -i .raw -pix_fmt output.png".""" + vollog.warning(warn_msg) + + # Prefer using the virtual resolution, instead of the visible one. + # This prevents missing non-visible data stored in the framebuffer. + fb = Framebuffer( + id, + xres_virtual=fb_info.var.xres_virtual, + yres_virtual=fb_info.var.yres_virtual, + line_length=fb_info.fix.line_length, + bpp=fb_info.var.bits_per_pixel, + size=fb_info.var.yres_virtual * fb_info.fix.line_length, + color_fields=color_fields, + fb_info=fb_info, + ) + + return fb + + def _generator(self): + kernel_name = self.config["kernel"] + kernel = self.context.modules[kernel_name] + + if not kernel.has_symbol("num_registered_fb"): + raise exceptions.SymbolError( + "num_registered_fb", + kernel.symbol_table_name, + "The provided symbol does not exist in the symbol table. This means you are either analyzing an unsupported kernel version or that your symbol table is corrupt.", + ) + + num_registered_fb = kernel.object_from_symbol("num_registered_fb") + if num_registered_fb < 1: + vollog.info("No registered framebuffer in the fbdev API.") + return None + + registered_fb = kernel.object_from_symbol("registered_fb") + fb_info_list = utility.array_of_pointers( + registered_fb, + num_registered_fb, + kernel.symbol_table_name + constants.BANG + "fb_info", + self.context, + ) + + for fb_info in fb_info_list: + fb = self.parse_fb_info(fb_info) + file_output = "Disabled" + if self.config["dump"]: + try: + file_output = self.dump_fb( + self.context, kernel_name, self.open, fb, bool(fb.color_fields) + ) + except exceptions.InvalidAddressException as excp: + vollog.error( + f'Layer {excp.layer_name} failed to read address {hex(excp.invalid_address)} when dumping framebuffer "{fb.id}".' + ) + file_output = "Error" + + try: + fb_device_name = utility.pointer_to_string( + fb.fb_info.dev.kobj.name, 256 + ) + except exceptions.InvalidAddressException: + fb_device_name = NotAvailableValue() + + yield ( + 0, + ( + format_hints.Hex(fb.fb_info.screen_base), + fb_device_name, + fb.id, + fb.size, + f"{fb.xres_virtual}x{fb.yres_virtual}", + fb.bpp, + "RUNNING" if fb.fb_info.state == 0 else "SUSPENDED", + str(file_output), + ), + ) + + def run(self): + columns = [ + ("Address", format_hints.Hex), + ("Device", str), + ("ID", str), + ("Size", int), + ("Virtual resolution", str), + ("BPP", int), + ("State", str), + ("Filename", str), + ] + + return TreeGrid( + columns, + self._generator(), + )