On Thu, Nov 8, 2018 at 1:06 PM Yu-cheng Yu [off-list ref] wrote:

On Thu, 2018-11-08 at 12:46 -0800, Andy Lutomirski wrote:

quoted

On Thu, Oct 11, 2018 at 8:20 AM Yu-cheng Yu [off-list ref] wrote:

quoted

Intel Control-flow Enforcement Technology (CET) introduces the
following MSRs into the XSAVES system states.

    IA32_U_CET (user-mode CET settings),
    IA32_PL3_SSP (user-mode shadow stack),
    IA32_PL0_SSP (kernel-mode shadow stack),
    IA32_PL1_SSP (ring-1 shadow stack),
    IA32_PL2_SSP (ring-2 shadow stack).

Signed-off-by: Yu-cheng Yu <redacted>
---
 arch/x86/include/asm/fpu/types.h            | 22 +++++++++++++++++++++
 arch/x86/include/asm/fpu/xstate.h           |  4 +++-
 arch/x86/include/uapi/asm/processor-flags.h |  2 ++
 arch/x86/kernel/fpu/xstate.c                | 10 ++++++++++
 4 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/fpu/types.h

b/arch/x86/include/asm/fpu/types.h
index 202c53918ecf..e55d51d172f1 100644

--- a/arch/x86/include/asm/fpu/types.h
+++ b/arch/x86/include/asm/fpu/types.h

@@ -114,6 +114,9 @@ enum xfeature {
        XFEATURE_Hi16_ZMM,
        XFEATURE_PT_UNIMPLEMENTED_SO_FAR,
        XFEATURE_PKRU,
+       XFEATURE_RESERVED,
+       XFEATURE_SHSTK_USER,
+       XFEATURE_SHSTK_KERNEL,

        XFEATURE_MAX,
 };

@@ -128,6 +131,8 @@ enum xfeature {
 #define XFEATURE_MASK_Hi16_ZMM         (1 << XFEATURE_Hi16_ZMM)
 #define XFEATURE_MASK_PT               (1 <<

XFEATURE_PT_UNIMPLEMENTED_SO_FAR)
 #define XFEATURE_MASK_PKRU             (1 << XFEATURE_PKRU)
+#define XFEATURE_MASK_SHSTK_USER       (1 << XFEATURE_SHSTK_USER)
+#define XFEATURE_MASK_SHSTK_KERNEL     (1 << XFEATURE_SHSTK_KERNEL)

 #define XFEATURE_MASK_FPSSE            (XFEATURE_MASK_FP |
XFEATURE_MASK_SSE)
 #define XFEATURE_MASK_AVX512           (XFEATURE_MASK_OPMASK \

@@ -229,6 +234,23 @@ struct pkru_state {
        u32                             pad;
 } __packed;

+/*
+ * State component 11 is Control flow Enforcement user states
+ */
+struct cet_user_state {
+       u64 u_cet;      /* user control flow settings */
+       u64 user_ssp;   /* user shadow stack pointer */
+} __packed;
+
+/*
+ * State component 12 is Control flow Enforcement kernel states
+ */
+struct cet_kernel_state {
+       u64 kernel_ssp; /* kernel shadow stack */
+       u64 pl1_ssp;    /* ring-1 shadow stack */
+       u64 pl2_ssp;    /* ring-2 shadow stack */
+} __packed;
+

Why are these __packed?  It seems like it'll generate bad code for no
obvious purpose.

That prevents any possibility that the compiler will insert padding, although in
64-bit kernel this should not happen to either struct.  Also all xstate
components here are packed.

They both seem like bugs, perhaps.  As I understand it, __packed
removes padding, but it also forces the compiler to expect the fields
to be unaligned even if they are actually aligned.