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Date: Tue, 8 Mar 2022 13:41:42 +0200
From: Jarkko Sakkinen <jarkko@...nel.org>
To: linux-mm@...ck.org, linux-fsdevel@...r.kernel.org
Cc: Dave Hansen <dave.hansen@...ux.intel.com>,
Nathaniel McCallum <nathaniel@...fian.com>,
Reinette Chatre <reinette.chatre@...el.com>,
Alexander Viro <viro@...iv.linux.org.uk>,
linux-sgx@...r.kernel.org, linux-kernel@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH RFC v3 3/3] x86/sgx: Implement EAUG population with
MAP_POPULATE
On Tue, Mar 08, 2022 at 01:28:33PM +0200, Jarkko Sakkinen wrote:
> With SGX1 an enclave needs to be created with its maximum memory demands
> pre-allocated. Pages cannot be added to an enclave after it is initialized.
> SGX2 introduces a new function, ENCLS[EAUG] for adding pages to an
> initialized enclave.
>
> Add support for dynamically adding pages to an initialized enclave with
> mmap() by populating pages with EAUG. Use f_ops->populate() callback to
> achieve this behaviour.
>
> Signed-off-by: Jarkko Sakkinen <jarkko@...nel.org>
> ---
> arch/x86/kernel/cpu/sgx/driver.c | 128 +++++++++++++++++++++++++++++++
> 1 file changed, 128 insertions(+)
>
> diff --git a/arch/x86/kernel/cpu/sgx/driver.c b/arch/x86/kernel/cpu/sgx/driver.c
> index aa9b8b868867..848938334e8a 100644
> --- a/arch/x86/kernel/cpu/sgx/driver.c
> +++ b/arch/x86/kernel/cpu/sgx/driver.c
> @@ -9,6 +9,7 @@
> #include <asm/traps.h>
> #include "driver.h"
> #include "encl.h"
> +#include "encls.h"
>
> u64 sgx_attributes_reserved_mask;
> u64 sgx_xfrm_reserved_mask = ~0x3;
> @@ -101,6 +102,132 @@ static int sgx_mmap(struct file *file, struct vm_area_struct *vma)
> return 0;
> }
>
> +static int sgx_encl_augment_page(struct sgx_encl *encl, unsigned long offset)
> +{
> + struct sgx_pageinfo pginfo = {0};
> + struct sgx_encl_page *encl_page;
> + struct sgx_epc_page *epc_page;
> + struct sgx_va_page *va_page;
> + u64 secinfo_flags;
> + int ret;
> +
> + /*
> + * Ignore internal permission checking for dynamically added pages.
> + * They matter only for data added during the pre-initialization phase.
> + * The enclave decides the permissions by the means of EACCEPT,
> + * EACCEPTCOPY and EMODPE.
> + */
> + secinfo_flags = SGX_SECINFO_R | SGX_SECINFO_W | SGX_SECINFO_X;
> + encl_page = sgx_encl_page_alloc(encl, offset, secinfo_flags);
> + if (IS_ERR(encl_page))
> + return PTR_ERR(encl_page);
> +
> + epc_page = sgx_alloc_epc_page(encl_page, true);
> + if (IS_ERR(epc_page)) {
> + ret = PTR_ERR(epc_page);
> + goto err_alloc_epc_page;
> + }
> +
> + va_page = sgx_encl_grow(encl);
> + if (IS_ERR(va_page)) {
> + ret = PTR_ERR(va_page);
> + goto err_grow;
> + }
> +
> + mutex_lock(&encl->lock);
> +
> + /*
> + * Adding to encl->va_pages must be done under encl->lock. Ditto for
> + * deleting (via sgx_encl_shrink()) in the error path.
> + */
> + if (va_page)
> + list_add(&va_page->list, &encl->va_pages);
> +
> + /*
> + * Insert prior to EADD in case of OOM. EADD modifies MRENCLAVE, i.e.
> + * can't be gracefully unwound, while failure on EADD/EXTEND is limited
> + * to userspace errors (or kernel/hardware bugs).
> + */
> + ret = xa_insert(&encl->page_array, PFN_DOWN(encl_page->desc),
> + encl_page, GFP_KERNEL);
> +
> + /*
> + * If ret == -EBUSY then page was created in another flow while
> + * running without encl->lock
> + */
> + if (ret)
> + goto err_xa_insert;
> +
> + pginfo.secs = (unsigned long)sgx_get_epc_virt_addr(encl->secs.epc_page);
> + pginfo.addr = encl_page->desc & PAGE_MASK;
> + pginfo.metadata = 0;
> +
> + ret = __eaug(&pginfo, sgx_get_epc_virt_addr(epc_page));
> + if (ret)
> + goto err_eaug;
> +
> + encl_page->encl = encl;
> + encl_page->epc_page = epc_page;
> + encl_page->type = SGX_PAGE_TYPE_REG;
> + encl->secs_child_cnt++;
> +
> + sgx_mark_page_reclaimable(encl_page->epc_page);
> +
> + mutex_unlock(&encl->lock);
> +
> + return 0;
> +
> +err_eaug:
> + xa_erase(&encl->page_array, PFN_DOWN(encl_page->desc));
> +
> +err_xa_insert:
> + sgx_encl_shrink(encl, va_page);
> + mutex_unlock(&encl->lock);
> +
> +err_grow:
> + sgx_encl_free_epc_page(epc_page);
> +
> +err_alloc_epc_page:
> + kfree(encl_page);
> +
> + return VM_FAULT_SIGBUS;
> +}
This can be obviously exported to be used also in the page fault handler.
> +
> +/*
> + * Add new pages to the enclave sequentially with ENCLS[EAUG]. Note that
> + * sgx_mmap() validates that the given VMA is within the enclave range. Calling
> + * here sgx_encl_may_map() second time would too time consuming.
> + */
> +static int sgx_populate(struct file *file, unsigned long start, unsigned long end)
> +{
> + struct sgx_encl *encl = file->private_data;
> + unsigned long length = end - start;
> + unsigned long pos;
> + int ret;
> +
> + /* EAUG works only for initialized enclaves. */
> + if (!test_bit(SGX_ENCL_INITIALIZED, &encl->flags))
> + return -EINVAL;
> +
> + for (pos = 0 ; pos < length; pos += PAGE_SIZE) {
> + if (signal_pending(current)) {
> + if (!pos)
> + ret = -ERESTARTSYS;
> +
> + break;
> + }
> +
> + if (need_resched())
> + cond_resched();
> +
> + ret = sgx_encl_augment_page(encl, start + pos);
> + if (ret)
> + break;
> + }
> +
> + return ret;
> +}
> +
> static unsigned long sgx_get_unmapped_area(struct file *file,
> unsigned long addr,
> unsigned long len,
> @@ -133,6 +260,7 @@ static const struct file_operations sgx_encl_fops = {
> .compat_ioctl = sgx_compat_ioctl,
> #endif
> .mmap = sgx_mmap,
> + .populate = sgx_populate,
> .get_unmapped_area = sgx_get_unmapped_area,
> };
>
> --
> 2.35.1
>
BR, Jarkko
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