Vulnerability CVE-2024-40974
Published: 2024-07-12

Description:
In the Linux kernel, the following vulnerability has been resolved:

powerpc/pseries: Enforce hcall result buffer validity and size

plpar_hcall(), plpar_hcall9(), and related functions expect callers to
provide valid result buffers of certain minimum size. Currently this
is communicated only through comments in the code and the compiler has
no idea.

For example, if I write a bug like this:

long retbuf[PLPAR_HCALL_BUFSIZE]; // should be PLPAR_HCALL9_BUFSIZE
plpar_hcall9(H_ALLOCATE_VAS_WINDOW, retbuf, ...);

This compiles with no diagnostics emitted, but likely results in stack
corruption at runtime when plpar_hcall9() stores results past the end
of the array. (To be clear this is a contrived example and I have not
found a real instance yet.)

To make this class of error less likely, we can use explicitly-sized
array parameters instead of pointers in the declarations for the hcall
APIs. When compiled with -Warray-bounds[1], the code above now
provokes a diagnostic like this:

error: array argument is too small;
is of size 32, callee requires at least 72 [-Werror,-Warray-bounds]
60 | plpar_hcall9(H_ALLOCATE_VAS_WINDOW, retbuf,
| ^ ~~~~~~

[1] Enabled for LLVM builds but not GCC for now. See commit
0da6e5fd6c37 ("gcc: disable '-Warray-bounds' for gcc-13 too") and
related changes.

 References:
https://git.kernel.org/stable/c/acf2b80c31c37acab040baa3cf5f19fbd5140b18
https://git.kernel.org/stable/c/19c166ee42cf16d8b156a6cb4544122d9a65d3ca
https://git.kernel.org/stable/c/a8c988d752b3d98d5cc1e3929c519a55ef55426c
https://git.kernel.org/stable/c/262e942ff5a839b9e4f3302a8987928b0c8b8a2d
https://git.kernel.org/stable/c/8aa11aa001576bf3b00dcb8559564ad7a3113588
https://git.kernel.org/stable/c/3ad0034910a57aa88ed9976b1431b7b8c84e0048
https://git.kernel.org/stable/c/aa6107dcc4ce9a3451f2d729204713783b657257
https://git.kernel.org/stable/c/ff2e185cf73df480ec69675936c4ee75a445c3e4
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