On 2021/12/24 21:18, Christophe Leroy wrote:

Le 24/12/2021 à 08:06, Kefeng Wang a écrit :

quoted

On 2021/12/24 14:01, Christophe Leroy wrote:

quoted

Le 23/12/2021 à 11:21, Kefeng Wang a écrit :

quoted

This reverts commit 517e1fbeb65f5eade8d14f46ac365db6c75aea9b.

     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

When run ethtool eth0, the BUG occurred, 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 PowerPC64, which leads to the panic, add back the
is_vmalloc_or_module()
check to fix it.

Is it expected that virt_addr_valid() returns true on PPC64 for
vmalloc'ed memory ? If that's the case it also means that
CONFIG_DEBUG_VIRTUAL won't work as expected either.

Our product reports this bug to me, after let them do some test,

I found virt_addr_valid return true for vmalloc'ed memory on their board.

I think DEBUG_VIRTUAL could not be work well too, but I can't test it.

quoted

If it is unexpected, I think you should fix PPC64 instead of adding this
hack back. Maybe the ARM64 fix can be used as a starting point, see
commit 68dd8ef32162 ("arm64: memory: Fix virt_addr_valid() using
__is_lm_address()")

Yes， I check the history,  fix virt_addr_valid() on PowerPC is what I
firstly want to do,

but I am not familiar with PPC, and also HARDENED_USERCOPY on other's
ARCHs could

has this issue too, so I add the workaround back.


1) PPC maintainer/expert, any suggestion ?

2) Maybe we could add some check to WARN this scenario.

--- a/mm/usercopy.c
+++ b/mm/usercopy.c

@@ -229,6 +229,8 @@ static inline void check_heap_object(const void

*ptr, unsigned long n,
          if (!virt_addr_valid(ptr))
                  return;

+       WARN_ON_ONCE(is_vmalloc_or_module_addr(ptr));

quoted

quoted

In the meantime, can you provide more information on your config,
especially which memory model is used ?

Some useful configs,

CONFIG_PPC64=y
CONFIG_PPC_BOOK3E_64=y
CONFIG_E5500_CPU=y
CONFIG_TARGET_CPU_BOOL=y
CONFIG_PPC_BOOK3E=y
CONFIG_E500=y
CONFIG_PPC_E500MC=y
CONFIG_PPC_FPU=y
CONFIG_FSL_EMB_PERFMON=y
CONFIG_FSL_EMB_PERF_EVENT=y
CONFIG_FSL_EMB_PERF_EVENT_E500=y
CONFIG_BOOKE=y
CONFIG_PPC_FSL_BOOK3E=y
CONFIG_PTE_64BIT=y
CONFIG_PHYS_64BIT=y
CONFIG_PPC_MMU_NOHASH=y
CONFIG_PPC_BOOK3E_MMU=y
CONFIG_SELECT_MEMORY_MODEL=y
CONFIG_FLATMEM_MANUAL=y
CONFIG_FLATMEM=y
CONFIG_FLAT_NODE_MEM_MAP=y
CONFIG_SPARSEMEM_VMEMMAP_ENABLE=y

OK so it is PPC64 book3e and with flatmem.

The problem is virt_to_pfn() which uses __pa()

__pa(x) on PPC64 is (x) & 0x0fffffffffffffffUL

And on book3e/64 we have

VMALLOC_START = KERN_VIRT_START = ASM_CONST(0x8000000000000000)


It means that __pa() will return a valid PFN for VMALLOCed addresses.


So an additional check is required in virt_addr_valid(), maybe check
that (kaddr & PAGE_OFFSET) == PAGE_OFFSET

Can you try that ?

#define virt_addr_valid(kaddr)	((kaddr & PAGE_OFFSET) == PAGE_OFFSET &&
pfn_valid(virt_to_pfn(kaddr)))

I got this commit,

commit 4dd7554a6456d124c85e0a4ad156625b71390b5c

Author: Nicholas Piggin [off-list ref]
Date:   Wed Jul 24 18:46:37 2019 +1000

     powerpc/64: Add VIRTUAL_BUG_ON checks for __va and __pa addresses

     Ensure __va is given a physical address below PAGE_OFFSET, and __pa is
     given a virtual address above PAGE_OFFSET.

It has check the PAGE_OFFSET in __pa,  will test it and resend the 
patch(with above warning changes).

Thanks.

Thanks
Christophe