Vulnerabilities

Lib-PSP iplloader (PRE-IPL)

NMI Backdoor

(Found by: Mathieulh, Proxima, C+D/Prometheus, Anyone spending time reverse engineering the pre-ipl) - Earliest discovery: 4/4/2007

Introduced: Tachyon 0x00140000 Boot rom

Fixed: Never

Vulnerable: Lib-PSP iplloader (all ROM Versions, 0.7.0 and newer Kbooti versions, PS Vita's PSP Bootrom)

The Lib-PSP iplloader rom (present within tachyon's IC package) as well as Lib-PSP iplloader versions 0.7.0 and onward feature a NMI/Interrupt handler backdoor (most likely used internally for debugging purposes) in its loader part at the very first instructions of the bootrom.

This backdoor allows anyone in control of the memory location address 0xBC100000 to perform a jump to an arbitrary location defined in coprocessor register $9

If 0xBC100000 is not equal to 0 and coprocessor register $9 is set, Lib-PSP iplloader will jump to the address set in the register very early in the code (by the 8th instruction). If 0xBC100000 is equal to 0, coprocessor register $9 will be reset back to 0.

Below are the relevant pieces of code:

ROM:BFC00004                 lw      $v0, 0xBC100000             # store 0xBC100000 to $v0
ROM:BFC0000C                 bnez    $v0, loc_BFC00064           # if $v0 (0xBC100000) is not equal to zero, jump to 0xBFC00064

ROM:BFC00064                 cfc0    $v0, $9                     # store coprocessor $9 to $v0
ROM:BFC00068                 beqz    $v0, loc_BFC00078 $         # if $v0 (coproc $9) is equal to 0 jump to 0xBFC00078
ROM:BFC0006C                 nop
ROM:BFC00070                 jr      $v0                         # jump to register $v0 (value initially set in coproc $9)

Because both address 0xBC100000 and coprocessor register $9 are controlled by syscon, this backdoor would allow an attacker performing a hardware based attack on syscon (by either replacing syscon or performing a man in the middle data injection) to set those values and gain Lib-PSP iplloader/pre-ipl time code execution (this requires using kernel code execution to fill memory with a payload to jump to beforehand), and thus potentially dump the pre-ipl code on newer targets.

Arbitrary Load Address

(Found by: C+D/Prometheus) - Earliest discovery: 4/4/2007

Introduced: Tachyon 0x00140000 Boot rom

Fixed: Never

Lib-PSP iplloader will not control the location at which it will load/copy the block, it will happily attempt to perform a memcpy (at a rate of 1 dword per cycle) to whatever load address is specified in the IPL header, assuming the header passes the checks (kirk1 hashes, HMAC-SHA1 (on 03g+)...) this allows to potentially write a payload at arbitrary locations.

Arbitrary Entrypoint Address

(Found by: C+D/Prometheus) - Earliest discovery: 4/4/2007

Introduced: Tachyon 0x00140000 Boot rom

Fixed: Lib-PSP iplloader 2.6.0

Lib-PSP iplloader will jump to any location specified in the last IPL block's entrypoint, this allows arbitrary execution, this was used in conjunction with the kirk time attack to craft a block and gain execution from at address 0xBFD00100 in the Pandora hack, and thus allowed to craft a "valid" block in a more timely fashion.

Lib-PSP iplloader always assumes a block with the checksum 0 is the first IPL block

(Found by: C+D/Prometheus) - Earliest discovery: Q4 2006

Introduced: Tachyon 0x00140000 Boot rom

Fixed: indirectly since 03g as no IPL that run on 03g and onwards have a block that uses a previous block checksum of 0 other than block0 itself.

This implementation fault has been exploited to create a memory hole in VRAM that could be filled with our own payload to gain execution and dump Lib-PSP iplloader.

3.5.0 Lib-PSP iplloader and later (applicable to 03g+ retail systems) do not perform the XOR Step when running in JIG/Service mode

(Found by: Mathieulh) - Earliest discovery: Q1 2019

This is not so much a vulnerability as a poor design implementation. To allow service centers to use a unique memory stick for multiple PSP models during servicing, Lib-PSP iplloader deliberately disables the XOR step, allowing a non xored IPL to run from Memory Stick. This is done so the IPL can run on all systems from 01g to 11g, this is also presumably done because XOR keys may differ in between tachyon revisions. This allows a potential attacker with the ability to enable JIG mode on a targeted PSP to bypass the XOR step and thus not requiring to know the XOR key to gain execution at IPL time (assuming all other checks (kirk1, HMAC, ECDSA... are passed).

3.5.0 Lib-PSP iplloader clears the XOR key after doing a cache sync during normal execution

(Found by: Proxima) - Earliest discovery: January 27th 2020

Introduced: Lib-PSP iplloader 3.5.0

Fixed: Never (this is the last known Lib-PSP iplloader revision for Development Tool.)

3.5.0 Lib-PSP iplloader clears the XOR key after doing a cache sync during normal execution, this allows to retrieve the key from the uncached memory at 0xA001088C. in JIG mode execution the key is cleared much earlier however resulting in the cache being synced once the key is already gone.

This allows to easily retrieve the key using an xored IPL block loaded at 0xBFE01000.