Re: [PATCH] x86/sgx: Avoid returning NULL in __sgx_alloc_epc_page()

[Borislav Petkov]

On Fri, Mar 19, 2021 at 05:06:02PM +1300, Kai Huang wrote:
> Below kernel bug happened when running simple SGX application when EPC
> is under pressure.  The root cause is with commit 5b8719504e3a
> ("x86/sgx: Add a basic NUMA allocation scheme to sgx_alloc_epc_page()"),
> __sgx_alloc_epc_page() returns NULL when there's no free EPC page can be
> allocated, while old behavior was it always returned ERR_PTR(-ENOMEM) in
> such case.
> 
> Fix by directly returning the page if __sgx_alloc_epc_page_from_node()
> allocates a valid page in fallback to non-local allocation, and always
> returning ERR_PTR(-ENOMEM) if no EPC page can be allocated.
> 
> [  253.474764] BUG: kernel NULL pointer dereference, address: 0000000000000008
> [  253.500101] #PF: supervisor write access in kernel mode
> [  253.525462] #PF: error_code(0x0002) - not-present page
> ...
> [  254.102041] Call Trace:
> [  254.126699]  sgx_ioc_enclave_add_pages+0x241/0x770
> [  254.151305]  sgx_ioctl+0x194/0x4b0
> [  254.174976]  ? handle_mm_fault+0xd0/0x260
> [  254.198470]  ? do_user_addr_fault+0x1ef/0x570
> [  254.221827]  __x64_sys_ioctl+0x91/0xc0
> [  254.244546]  do_syscall_64+0x38/0x90
> [  254.266728]  entry_SYSCALL_64_after_hwframe+0x44/0xae
> [  254.289232] RIP: 0033:0x7fdc4cf4031b
> ...
> [  254.711480] CR2: 0000000000000008
> [  254.735494] ---[ end trace 970dce6d4cdf7f64 ]---
> [  254.759915] RIP: 0010:sgx_alloc_epc_page+0x46/0x152
> ...
> 
> Fixes: 5b8719504e3a("x86/sgx: Add a basic NUMA allocation scheme to sgx_alloc_epc_page()")
> Signed-off-by: Kai Huang <kai.huang@xxxxxxxxx>
> ---
>  arch/x86/kernel/cpu/sgx/main.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)

I was on the verge whether to merge that into the original patch since
it is the top patch on the branch or create a new one but opted for
former because this way it won't break bisection and people won't have
to pay attention whether there's a fix patch to the NUMA patch too, in
case they wanna backport and whatnot.

Here's the new version:

Thx.

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