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    Subject[PATCH v2 1/2] x86: sgx_vepc: extract sgx_vepc_remove_page
    Date
    For bare-metal SGX on real hardware, the hardware provides guarantees
    SGX state at reboot. For instance, all pages start out uninitialized.
    The vepc driver provides a similar guarantee today for freshly-opened
    vepc instances, but guests such as Windows expect all pages to be in
    uninitialized state on startup, including after every guest reboot.

    One way to do this is to simply close and reopen the /dev/sgx_vepc file
    descriptor and re-mmap the virtual EPC. However, this is problematic
    because it prevents sandboxing the userspace (for example forbidding
    open() after the guest starts; this is doable with heavy use of SCM_RIGHTS
    file descriptor passing).

    In order to implement this, we will need a ioctl that performs
    EREMOVE on all pages mapped by a /dev/sgx_vepc file descriptor:
    other possibilities, such as closing and reopening the device,
    are racy.

    Start the implementation by creating a separate function with just
    the __eremove wrapper.

    Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
    ---
    v1->v2: keep WARN in sgx_vepc_free_page

    arch/x86/kernel/cpu/sgx/virt.c | 12 +++++++-----
    1 file changed, 7 insertions(+), 5 deletions(-)

    diff --git a/arch/x86/kernel/cpu/sgx/virt.c b/arch/x86/kernel/cpu/sgx/virt.c
    index 64511c4a5200..59cdf3f742ac 100644
    --- a/arch/x86/kernel/cpu/sgx/virt.c
    +++ b/arch/x86/kernel/cpu/sgx/virt.c
    @@ -111,10 +111,8 @@ static int sgx_vepc_mmap(struct file *file, struct vm_area_struct *vma)
    return 0;
    }

    -static int sgx_vepc_free_page(struct sgx_epc_page *epc_page)
    +static int sgx_vepc_remove_page(struct sgx_epc_page *epc_page)
    {
    - int ret;
    -
    /*
    * Take a previously guest-owned EPC page and return it to the
    * general EPC page pool.
    @@ -124,7 +122,12 @@ static int sgx_vepc_free_page(struct sgx_epc_page *epc_page)
    * case that a guest properly EREMOVE'd this page, a superfluous
    * EREMOVE is harmless.
    */
    - ret = __eremove(sgx_get_epc_virt_addr(epc_page));
    + return __eremove(sgx_get_epc_virt_addr(epc_page));
    +}
    +
    +static int sgx_vepc_free_page(struct sgx_epc_page *epc_page)
    +{
    + int ret = sgx_vepc_remove_page(epc_page);
    if (ret) {
    /*
    * Only SGX_CHILD_PRESENT is expected, which is because of
    @@ -144,7 +147,6 @@ static int sgx_vepc_free_page(struct sgx_epc_page *epc_page)
    }

    sgx_free_epc_page(epc_page);
    -
    return 0;
    }

    --
    2.27.0

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