[PATCH v11 16/37] x86/ptrace: Add FRED additional information to the pt_regs structure

Xin Li
2023-09-23T10:11:56Z

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@zytor.com>
Tested-by: Shan Kang <shan.kang@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Xin Li <xin3.li@intel.com>
---

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