linux-kernel - [PATCH v10 16/38] x86/ptrace: Add FRED additional information to the pt

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Message-Id: <20230914044805.301390-17-xin3.li@intel.com>
Date:   Wed, 13 Sep 2023 21:47:43 -0700
From:   Xin Li <xin3.li@...el.com>
To:     linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-edac@...r.kernel.org, linux-hyperv@...r.kernel.org,
        kvm@...r.kernel.org, xen-devel@...ts.xenproject.org
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
        luto@...nel.org, pbonzini@...hat.com, seanjc@...gle.com,
        peterz@...radead.org, jgross@...e.com, ravi.v.shankar@...el.com,
        mhiramat@...nel.org, andrew.cooper3@...rix.com,
        jiangshanlai@...il.com
Subject: [PATCH v10 16/38] x86/ptrace: Add FRED additional information to the pt_regs structure

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@...or.com>
Tested-by: Shan Kang <shan.kang@...el.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Xin Li <xin3.li@...el.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