[PATCH v10 16/38] x86/ptrace: Add FRED additional information to the pt_regs structure

[Xin Li <xin3.li@xxxxxxxxx>]

FRED defines additional information in the upper 48 bits of cs/ss
fields. Therefore add the information definitions into the pt_regs
structure.

Specially introduce a new structure fred_ss to denote the FRED flags
above SS selector, which avoids FRED_SSX_ macros and makes the code
simpler and easier to read.

Signed-off-by: H. Peter Anvin (Intel) <hpa@xxxxxxxxx>
Tested-by: Shan Kang <shan.kang@xxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Xin Li <xin3.li@xxxxxxxxx>
---

Changes since v9:
* Introduce a new structure fred_ss to denote the FRED flags above SS
  selector, which avoids FRED_SSX_ macros and makes the code simpler
  and easier to read (Thomas Gleixner).
* Use type u64 to define FRED bit fields instead of type unsigned int
  (Thomas Gleixner).

Changes since v8:
* Reflect stack frame definition changes from FRED spec 3.0 to 5.0.
* Use __packed instead of __attribute__((__packed__)) (Borislav Petkov).
* Put all comments above the members, like the rest of the file does
  (Borislav Petkov).

Changes since v3:
* Rename csl/ssl of the pt_regs structure to csx/ssx (x for extended)
  (Andrew Cooper).
---
 arch/x86/include/asm/ptrace.h | 51 +++++++++++++++++++++++++++++++----
 1 file changed, 46 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/ptrace.h b/arch/x86/include/asm/ptrace.h
index f08ea073edd6..5786c8ca5f4c 100644
--- a/arch/x86/include/asm/ptrace.h
+++ b/arch/x86/include/asm/ptrace.h
@@ -56,6 +56,25 @@ struct pt_regs {
 
 #else /* __i386__ */
 
+struct fred_ss {
+       u64     ss      : 16,   // SS selector
+               sti     :  1,   // STI state
+               swevent :  1,   // Set if syscall, sysenter or INT n
+               nmi     :  1,   // Event is NMI type
+                       : 13,
+               vector  :  8,   // Event vector
+                       :  8,
+               type    :  4,   // Event type
+                       :  4,
+               enclave :  1,   // Event was incident to enclave execution
+               lm      :  1,   // CPU was in long mode
+               nested  :  1,   // Nested exception during FRED delivery
+                               // not set for #DF
+                       :  1,
+               insnlen :  4;   // The length of the instruction causing the 
event
+                               // Only set for INT0, INT1, INT3, INT n, SYSCALL
+};                             // and SYSENTER. 0 otherwise.
+
 struct pt_regs {
        /*
         * C ABI says these regs are callee-preserved. They aren't saved on
@@ -85,6 +104,12 @@ struct pt_regs {
         * - the syscall number (syscall, sysenter, int80)
         * - error_code stored by the CPU on traps and exceptions
         * - the interrupt number for device interrupts
+        *
+        * A FRED stack frame starts here:
+        *   1) It _always_ includes an error code;
+        *
+        *   2) The return frame for ERET[US] starts here, but
+        *      the content of orig_ax is ignored.
         */
        unsigned long orig_ax;
 
@@ -92,20 +117,36 @@ struct pt_regs {
        unsigned long ip;
 
        union {
-               u64     csx;    // The full 64-bit data slot containing CS
-               u16     cs;     // CS selector
+               u64     csx;            // The full data for FRED
+               /*
+                * The 'cs' member should be defined as a 16-bit bit-field
+                * along with the 'sl' and 'wfe' members, which however
+                * breaks compiling REG_OFFSET_NAME(cs), because compilers
+                * disallow calculating the address of a bit-field.
+                *
+                * Therefore 'cs" is defined as an individual member with
+                * type u16.
+                */
+               u16     cs;             // CS selector
+               u64             : 16,
+                       sl      :  2,   // Stack level at event time
+                       wfe     :  1,   // IBT is in WAIT_FOR_BRANCH_STATE
+                               : 45;
        };
 
        unsigned long flags;
        unsigned long sp;
 
        union {
-               u64     ssx;    // The full 64-bit data slot containing SS
-               u16     ss;     // SS selector
+               u64             ssx;            // The full data for FRED
+               u16             ss;             // SS selector
+               struct fred_ss  fred_ss;        // The fred extension
        };
 
        /*
-        * Top of stack on IDT systems.
+        * Top of stack on IDT systems, while FRED systems have extra fields
+        * defined above for storing exception related information, e.g. CR2 or
+        * DR6.
         */
 };
 
-- 
2.34.1