On Wed, 2018-07-11 at 12:45 -0700, Jann Horn wrote:

On Tue, Jul 10, 2018 at 3:31 PM Yu-cheng Yu [off-list ref]
wrote:

quoted

arch_prctl(ARCH_CET_STATUS, unsigned long *addr)
    Return CET feature status.

    The parameter 'addr' is a pointer to a user buffer.
    On returning to the caller, the kernel fills the following
    information:

    *addr = SHSTK/IBT status
    *(addr + 1) = SHSTK base address
    *(addr + 2) = SHSTK size

arch_prctl(ARCH_CET_DISABLE, unsigned long features)
    Disable SHSTK and/or IBT specified in 'features'.  Return
-EPERM
    if CET is locked out.

arch_prctl(ARCH_CET_LOCK)
    Lock out CET feature.

arch_prctl(ARCH_CET_ALLOC_SHSTK, unsigned long *addr)
    Allocate a new SHSTK.

    The parameter 'addr' is a pointer to a user buffer and
indicates
    the desired SHSTK size to allocate.  On returning to the caller
    the buffer contains the address of the new SHSTK.

arch_prctl(ARCH_CET_LEGACY_BITMAP, unsigned long *addr)
    Allocate an IBT legacy code bitmap if the current task does not
    have one.

    The parameter 'addr' is a pointer to a user buffer.
    On returning to the caller, the kernel fills the following
    information:

    *addr = IBT bitmap base address
    *(addr + 1) = IBT bitmap size

Signed-off-by: H.J. Lu <redacted>
Signed-off-by: Yu-cheng Yu <redacted>

[...]

quoted

diff --git a/arch/x86/kernel/cet_prctl.c

b/arch/x86/kernel/cet_prctl.c
new file mode 100644
index 000000000000..86bb78ae656d

--- /dev/null
+++ b/arch/x86/kernel/cet_prctl.c

@@ -0,0 +1,141 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#include <linux/errno.h>
+#include <linux/uaccess.h>
+#include <linux/prctl.h>
+#include <linux/compat.h>
+#include <asm/processor.h>
+#include <asm/prctl.h>
+#include <asm/elf.h>
+#include <asm/elf_property.h>
+#include <asm/cet.h>
+
+/* See Documentation/x86/intel_cet.txt. */
+
+static int handle_get_status(unsigned long arg2)
+{
+       unsigned int features = 0;
+       unsigned long shstk_base, shstk_size;
+
+       if (current->thread.cet.shstk_enabled)
+               features |= GNU_PROPERTY_X86_FEATURE_1_SHSTK;
+       if (current->thread.cet.ibt_enabled)
+               features |= GNU_PROPERTY_X86_FEATURE_1_IBT;
+
+       shstk_base = current->thread.cet.shstk_base;
+       shstk_size = current->thread.cet.shstk_size;
+
+       if (in_ia32_syscall()) {
+               unsigned int buf[3];
+
+               buf[0] = features;
+               buf[1] = (unsigned int)shstk_base;
+               buf[2] = (unsigned int)shstk_size;
+               return copy_to_user((unsigned int __user *)arg2,

buf,
+                                   sizeof(buf));
+       } else {
+               unsigned long buf[3];
+
+               buf[0] = (unsigned long)features;
+               buf[1] = shstk_base;
+               buf[2] = shstk_size;
+               return copy_to_user((unsigned long __user *)arg2,
buf,
+                                   sizeof(buf));
+       }

Other places in the kernel (e.g. the BPF subsystem) just
unconditionally use u64 instead of unsigned long to avoid having to
switch between different sizes. I wonder whether that would make
sense
here?

Yes, that simplifies the code.  I will make that change.

Yu-cheng
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