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>
Reviewed-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>
> ---
> arch/x86/kernel/cpu/sgx/main.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
> index fe26e7e91c25..7105e34da530 100644
> --- a/arch/x86/kernel/cpu/sgx/main.c
> +++ b/arch/x86/kernel/cpu/sgx/main.c
> @@ -508,10 +508,10 @@ struct sgx_epc_page *__sgx_alloc_epc_page(void)
>
> page = __sgx_alloc_epc_page_from_node(nid);
> if (page)
> - break;
> + return page;
> }
>
> - return page;
> + return ERR_PTR(-ENOMEM);
> }
>
> /**
> --
> 2.30.2
>
>
/Jarkko
