3DS System Flaws

From 3dbrew
Jump to navigation Jump to search

Exploits are used to execute unofficial code (homebrew) on the Nintendo 3DS. This page is a list of known 3DS-mode exploits.

List of 3DS exploits

Current Efforts

There are people working on finding exploits and documenting the 3DS. Here's a list of some current efforts being made to make homebrew on the 3DS possible:

  • See here regarding Ninjhax.

Stale / Rejected Efforts

  • Neimod has been working on a RAM dumping setup for a little while now. He's de-soldered the 3DS's RAM chip and hooked it and the RAM pinouts on the 3DS' PCB up to a custom RAM dumping setup. Recent photos show that the setup is working quite well, with the 3DS successfully booting up. Pictures of neimod's work can be found on his Flickr stream.
     Neimod's flickr stream is now private and his work is considered awesome.
  • A loser (who will remain unnamed) has released CFW and CIA installers along with other stolen and illegal stuff.

Failed attempts

Here are listed all attempts at exploiting 3DS software that have failed so far.

  • Pushmo (3DSWare), QR codes: level name is properly limited to 16 characters, game doesn't crash with a longer name. The only possible crashes are triggered by out-of-bounds array index values, these crashes are not exploitable.

  • Pyramids (3DSWare), QR codes: no strings. Only crashes are from out-of-bounds values (like background ID) and are not exploitable.

  • 3DS browser, 2^32 characters long string: this is similar to the vulnerability fixed here, concat-large-strings-crash2.html triggers a crash which is about the same as the one triggered by a 2^32 string. Most of the time this vulnerability will cause a memory page permissions fault, since the WebKit code attempts to copy the string text data to the output buffer located in read-only CRO heap memory. The only difference between a crash triggered by a 2^32 string and the concat-large-strings-crash2.html crash is at the former copies the string data using the original string length(like 1 text character for "x", 4 for "xxxx") while the latter attempts to copy >12MB. In some very rare cases a thread separate from the string data-copy thread will crash, this might be exploitable. However, this is mostly useless since it rarely crashes this way.

Tips and info

The 3DS uses the XN feature of the ARM processor, and only apps that have the necessary permissions in their headers can set memory to be executable. This means that although a usable buffer overflow exploit would still be useful, it would not go the entire way towards allowing code to be run in an easy or practical fashion (like an actual homebrew launcher). For that, an exploit in the system is required. A buffer overflow exploit does, however, provide enough wiggle room through the use of return-oriented programming to potentially trigger a system exploit.

SD card extdata and SD savegames can be attacked, for consoles where the console-unique movable.sed was dumped.

Note that the publicly-available <v5.0 total-control exploits are Process9 exploits, not "kernel exploits".

System flaws

FIRM Process9

Summary Description Successful exploitation result Fixed in system version Last FIRM version this was flaw was checked for Timeframe this was discovered
This can't be exploited from ARM11 userland. ARM9 code execution None 9.3.0-X 2012

ARM11 kernel

Summary Description Successful exploitation result Fixed in system version Last FIRM version this was flaw was checked for Timeframe this was discovered
SVC table too small The table of function pointers for SVC's only contains entries up to 0x7D, but the biggest allowed SVC for the table is 0x7F. Thus, executing SVC7E or SVC7F would make the SVC-handler read after the buffer, and interpret some ARM instructions as function pointers.

However, this would require patching the kernel .text or modifying SVC-access-control. Even if you could get these to execute, they would still jump to memory that isn't mapped as executable.

None 9.3.0-21 2012
svcBackdoor (0x7B) This backdoor allows executing SVC-mode code at the user-specified code-address. This is used by Process9, using this on the ARM11(with NATIVE_FIRM) requires patching the kernel .text or modifying SVC-access-control. See description None 9.3.0-21
0xEFF00000 / 0xDFF00000 ARM11 kernel virtual-memory The ARM11 kernel-mode 0xEFF00000/0xDFF00000 virtual-memory(size 0x100000) is mapped to phys-mem 0x1FF00000(entire DSP-mem + entire AXIWRAM), with permissions RW-. This is used during ARM11 kernel startup, this never seems to be used after that, however. None 9.3.0-21
When combined with other flaws: ARM11-kernelmode code execution 9.3.0-21 February 2014
PXI Command input/output buffer permissions Originally the ARM11-kernel didn't check permissions for PXI input/output buffers for commands. Starting with 6.0.0 PXI input/output buffers must have RW permissions, otherwise kernelpanic is triggered. 6.0.0-11 2012
svcStartInterProcessDma For svcStartInterProcessDma, the kernel code had the following flaws:
  • Originally the ARM11-kernel read the input DmaConfig structure directly in kernel-mode(ldr(b/h) instructions), without checking whether the DmaConfig address is readable under userland. This was fixed by copying that structure to the SVC-mode stack, using the ldrbt instruction.
  • Integer overflows for srcaddr+size and dstaddr+size are now checked(with 6.0.0-11), which were not checked before.
  • The kernel now also checks whether the srcaddr/dstaddr (+size) is within userland memory (0x20000000), the kernel now (with 6.0.0-11) returns an error when the address is beyond userland memory. Using an address >=0x20000000 would result in the kernel reading from the process L1 MMU table, beyond the memory allocated for that MMU table(for vaddr->physaddr conversion).
6.0.0-11 DmaConfig issue: unknown. The rest: 2014
svcControlMemory Parameter checks For svcControlMemory the parameter check had these two flaws:
  • The allowed range for addr0, addr1, size parameters depends on which MemoryOperation is being specified. The limitation for GSP heap was only checked if op=(u32)0x10003. By setting a random bit in op that has no meaning (like bit17?), op would instead be (u32)0x30003, and the range-check would be less strict and not accurate. However, the kernel doesn't actually use the input address for LINEAR memory-mapping at all besides the range-checks, so this isn't actually useful. This was fixed in the kernel by just checking for the LINEAR bit, instead of comparing the entire MemoryOperation value with 0x10003.
  • Integer overflows on (addr0+size) are now checked that previously weren't (this also applies to most other address checks elsewhere in the kernel).
Command request/response buffer overflow Originally the kernel did not check the word-values from the command-header. Starting with 5.0.0-11, the kernel will trigger a kernelpanic() when the total word-size of the entire command(including the cmd-header) is larger than 0x40-words (0x100-bytes). This allows overwriting threadlocalstorage+0x180 in the destination thread. However, since the data written there would be translate parameters (such as header-words + buffer addresses), exploiting this would likely be very difficult, if possible at all.

If the two words at threadlocalstorage+0x180 could be overwritten with controlled data this way, one could then use a command with a buffer-header of ((size<<14) | 2) to write arbitrary memory to any RW userland memory in the destination process.

5.0.0-11 v4.1 FIRM -> v5.0 code diff
SVC stack allocation overflows
  • Syscalls that allocate a variable-length array on stack, only checked bit31 before multiplying by 4/16 (when calculating how much memory to allocate). If a large integer was passed as input to one of these syscalls, an integer overflow would occur, and too little memory would have been allocated on stack resulting in a buffer overrun.
  • The alignment (size+7)&~7 calculation before allocation was not checked for integer overflow.

This might allow for ARM11 kernel code-execution.

(Applies to svcSetResourceLimitValues, svcGetThreadList, svcGetProcessList, svcReplyAndReceive, svcWaitSynchronizationN.)

5.0.0-11 v4.1 FIRM -> v5.0 code diff
svcControlMemory MemoryOperation MAP memory-permissions svcControlMemory with MemoryOperation=MAP allows mapping the already-mapped process virtual-mem at addr1, to addr0. The lowest address permitted for addr1 is 0x00100000. Originally the ARM11 kernel didn't check memory permissions for addr1. Therefore .text as addr1 could be mapped elsewhere as RW- memory, which allowed ARM11 userland code-execution. 4.1.0-8 2012
Command input/output buffer permissions Originally the ARM11 kernel didn't check memory permissions for the input/output buffers for commands. Starting with 4.0.0-7 the ARM11 kernel will trigger a kernelpanic() if the input/output buffers don't have the required memory permissions. For example, this allowed a FSUSER file-read to .text, which therefore allowed ARM11-userland code execution. 4.0.0-7 2012
svcReadProcessMemory/svcWriteProcessMemory memory permissions Originally the kernel only checked the first page(0x1000-bytes) of the src/dst buffers, for svcReadProcessMemory and svcWriteProcessMemory. There is no known retail processes which have access to these SVCs. 4.0.0-7 2012?

FIRM ARM11 modules

Summary Description Fixed in system version
"srv:pm" process registration Originally any process had access to the port "srv:pm". The PID's used for the (un)registration commands are not checked either. This allowed any process to re-register itself with "srv:pm", and therefore allowed the process to give itself access to any service, bypassing the exheader service-access-control list.

This was fixed in 7.0.0-13: starting with 7.0.0-13 "srv:pm" is now a service instead of a globally accessible port. Only processes with PID's less than 6 (in other words: fs, ldr, sm, pm, pxi modules) have access to it. With 7.0.0-13 there can only be one session for "srv:pm" open at a time(this is used by pm module), svcBreak will be executed if more sessions are opened by the processes which can access this.

This flaw was needed for exploiting the <=v4.x Process9 PXI vulnerabilities from ARM11 userland ROP, since most applications don't have access to those service(s).


ARM11 system modules

ARM11 system applications and applets

Summary Description Fixed in system version
3DS System Settings DS profile string stack-smash Too long or corrupted strings (01Ah 2 Nickname length in characters 050h 2 Message length in characters) in the NVRAM DS user settings (System Settings->Other Settings->Profile->Nintendo DS Profile) cause it to crash in 3DS-mode due to a stack-smash. The DSi is not vulnerable to this, DSi launcher(menu) and DSi System Settings will reset the NVRAM user-settings if the length field values are too long(same result as when the CRCs are invalid). TWL_FIRM also resets the NVRAM user-settings when the string-length(s) are too long. 7.0.0-13