CVE-2022-49067

Summary

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

powerpc: Fix virt_addr_valid() for 64-bit Book3E & 32-bit

mpe: On 64-bit Book3E vmalloc space starts at 0x8000000000000000.

Because of the way __pa() works we have: __pa(0x8000000000000000) == 0, and therefore virt_to_pfn(0x8000000000000000) == 0, and therefore virt_addr_valid(0x8000000000000000) == true

Which is wrong, virt_addr_valid() should be false for vmalloc space. In fact all vmalloc addresses that alias with a valid PFN will return true from virt_addr_valid(). That can cause bugs with hardened usercopy as described below by Kefeng Wang:

When running ethtool eth0 on 64-bit Book3E, a BUG occurred:

usercopy: Kernel memory exposure attempt detected from SLUB object not in SLUB page?! (offset 0, size 1048)!
kernel BUG at mm/usercopy.c:99
...
usercopy_abort+0x64/0xa0 (unreliable)
__check_heap_object+0x168/0x190
__check_object_size+0x1a0/0x200
dev_ethtool+0x2494/0x2b20
dev_ioctl+0x5d0/0x770
sock_do_ioctl+0xf0/0x1d0
sock_ioctl+0x3ec/0x5a0
__se_sys_ioctl+0xf0/0x160
system_call_exception+0xfc/0x1f0
system_call_common+0xf8/0x200

The code shows below,

data = vzalloc(array_size(gstrings.len, ETH_GSTRING_LEN));
copy_to_user(useraddr, data, gstrings.len * ETH_GSTRING_LEN))

The data is alloced by vmalloc(), virt_addr_valid(ptr) will return true on 64-bit Book3E, which leads to the panic.

As commit 4dd7554a6456 ("powerpc/64: Add VIRTUAL_BUG_ON checks for __va and __pa addresses") does, make sure the virt addr above PAGE_OFFSET in the virt_addr_valid() for 64-bit, also add upper limit check to make sure the virt is below high_memory.

Meanwhile, for 32-bit PAGE_OFFSET is the virtual address of the start of lowmem, high_memory is the upper low virtual address, the check is suitable for 32-bit, this will fix the issue mentioned in commit 602946ec2f90 ("powerpc: Set max_mapnr correctly") too.

On 32-bit there is a similar problem with high memory, that was fixed in commit 602946ec2f90 ("powerpc: Set max_mapnr correctly"), but that commit breaks highmem and needs to be reverted.

We can't easily fix __pa(), we have code that relies on its current behaviour. So for now add extra checks to virt_addr_valid().

For 64-bit Book3S the extra checks are not necessary, the combination of virt_to_pfn() and pfn_valid() should yield the correct result, but they are harmless.

[mpe: Add additional change log detail]

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/deab81144d5a043f42804207fb76cfbd8a806978
• https://git.kernel.org/stable/c/d36febbcd537fcc50284e8b89609632d0146529f
• https://git.kernel.org/stable/c/fddb88bd266f4513abab7c36bca98935c9148a98
• https://git.kernel.org/stable/c/a3727c25eacd7e437c4f560957fa3a376fe93e6b
• https://git.kernel.org/stable/c/cbc065efcba000ad8f615f506ebe61b6d3c5145b
• https://git.kernel.org/stable/c/ffa0b64e3be58519ae472ea29a1a1ad681e32f48

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