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SubjectRe: [PATCH v3 1/7] x86/sgx: Provide indication of life-cycle of EPC pages
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On 7/28/21 1:46 PM, Tony Luck wrote:
> +++ b/arch/x86/kernel/cpu/sgx/main.c
> @@ -581,7 +581,7 @@ struct sgx_epc_page *sgx_alloc_epc_page(void *owner, bool reclaim)
> for ( ; ; ) {
> page = __sgx_alloc_epc_page();
> if (!IS_ERR(page)) {
> - page->owner = owner;
> + page->owner = owner ? owner : page;
> break;
> }

I'm a little worried about this.

Let's say we get confused about the type of the page and dereference
page->owner. If it's NULL, we get a nice oops. If it's a real, valid
pointer, we get real valid memory back that we can scribble on.

Wouldn't it be safer to do something like:

page->owner = owner ? owner : (void *)-1;

-1 is non-NULL, but also invalid, which makes it harder for us to poke
ourselves in the eye.

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