[xen master] x86: Drop the vm86 segments selectors from struct cpu_user_regs

[patchbot@xxxxxxx]

commit 3c66a25672b4943a5a51d52f57038cdad6f9349e
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Sun Dec 29 14:46:34 2024 +0000
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Fri Aug 8 13:23:11 2025 +0100

    x86: Drop the vm86 segments selectors from struct cpu_user_regs
    
    The data segment registers are part of the on-stack IRET frame when
    interrupting Virtual 8086 mode, but this ceased being relevant for Xen in
    commit 5d1181a5ea5e ("xen: Remove x86_32 build target.") in 2012.
    
    With all other cleanup in place, delete the fields so we can introduce FRED
    support which uses this space for different data.
    
    Everywhere which used the es field as an offset in cpu_user_regs needs
    adjusting.  However, they'll change again for FRED, so no cleanup is 
performed
    at this juncture.
    
    This also undoes the OoB Read workaround in show_registers(), which can now
    switch back to being simple structure copy.
    
    No functional change, but a lot of rearranging of stack and struct layout
    under the hood.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/cpu/common.c                | 2 +-
 xen/arch/x86/include/asm/cpu-user-regs.h | 5 -----
 xen/arch/x86/include/asm/current.h       | 8 ++++----
 xen/arch/x86/include/asm/hvm/hvm.h       | 4 ----
 xen/arch/x86/include/asm/regs.h          | 3 +--
 xen/arch/x86/traps.c                     | 2 +-
 xen/arch/x86/x86_64/asm-offsets.c        | 2 +-
 xen/arch/x86/x86_64/traps.c              | 8 +-------
 8 files changed, 9 insertions(+), 25 deletions(-)

diff --git a/xen/arch/x86/cpu/common.c b/xen/arch/x86/cpu/common.c
index e063fe790a..97bdda1d4a 100644
--- a/xen/arch/x86/cpu/common.c
+++ b/xen/arch/x86/cpu/common.c
@@ -959,7 +959,7 @@ void load_system_tables(void)
         * Defer checks until exception support is sufficiently set up.
         */
        BUILD_BUG_ON((sizeof(struct cpu_info) -
-                     offsetof(struct cpu_info, guest_cpu_user_regs.es)) & 0xf);
+                     sizeof(struct cpu_user_regs)) & 0xf);
        BUG_ON(system_state != SYS_STATE_early_boot && (stack_bottom & 0xf));
 }
 
diff --git a/xen/arch/x86/include/asm/cpu-user-regs.h 
b/xen/arch/x86/include/asm/cpu-user-regs.h
index 0e78e38ed0..d700a3ef34 100644
--- a/xen/arch/x86/include/asm/cpu-user-regs.h
+++ b/xen/arch/x86/include/asm/cpu-user-regs.h
@@ -53,11 +53,6 @@ struct cpu_user_regs
      * For IDT delivery, tss->rsp0 points to this boundary as embedded within
      * struct cpu_info.  It must be 16-byte aligned.
      */
-
-    uint16_t es, _pad3[3];
-    uint16_t ds, _pad4[3];
-    uint16_t fs, _pad5[3];
-    uint16_t gs, _pad6[3];
 };
 
 #endif /* X86_CPU_USER_REGS_H */
diff --git a/xen/arch/x86/include/asm/current.h 
b/xen/arch/x86/include/asm/current.h
index 243d17ef79..a7c9473428 100644
--- a/xen/arch/x86/include/asm/current.h
+++ b/xen/arch/x86/include/asm/current.h
@@ -106,12 +106,12 @@ static inline struct cpu_info *get_cpu_info(void)
 #define get_per_cpu_offset()  (get_cpu_info()->per_cpu_offset)
 
 /*
- * Get the bottom-of-stack, as stored in the per-CPU TSS. This actually points
- * into the middle of cpu_info.guest_cpu_user_regs, at the section that
- * precisely corresponds to a CPU trap frame.
+ * Get the bottom-of-stack, as stored in the per-CPU TSS. This points at the
+ * end of cpu_info.guest_cpu_user_regs, at the section that precisely
+ * corresponds to a CPU trap frame.
  */
 #define get_stack_bottom()                      \
-    ((unsigned long)&get_cpu_info()->guest_cpu_user_regs.es)
+    ((unsigned long)(&get_cpu_info()->guest_cpu_user_regs + 1))
 
 /*
  * Get the reasonable stack bounds for stack traces and stack dumps.  Stack
diff --git a/xen/arch/x86/include/asm/hvm/hvm.h 
b/xen/arch/x86/include/asm/hvm/hvm.h
index bf8bc2e100..18e40910ff 100644
--- a/xen/arch/x86/include/asm/hvm/hvm.h
+++ b/xen/arch/x86/include/asm/hvm/hvm.h
@@ -624,10 +624,6 @@ static inline void hvm_sanitize_regs_fields(struct 
cpu_user_regs *regs,
     regs->saved_upcall_mask = 0xbf;
     regs->cs = 0xbeef;
     regs->ss = 0xbeef;
-    regs->ds = 0xbeef;
-    regs->es = 0xbeef;
-    regs->fs = 0xbeef;
-    regs->gs = 0xbeef;
 #endif
 }
 
diff --git a/xen/arch/x86/include/asm/regs.h b/xen/arch/x86/include/asm/regs.h
index ce9b028276..72595110e2 100644
--- a/xen/arch/x86/include/asm/regs.h
+++ b/xen/arch/x86/include/asm/regs.h
@@ -23,8 +23,7 @@
     (!is_pv_32bit_vcpu(v) ? ((tb)->eip == 0) : (((tb)->cs & ~3) == 0))
 
 /* Number of bytes of on-stack execution state to be context-switched. */
-/* NB. Segment registers and bases are not saved/restored on x86/64 stack. */
-#define CTXT_SWITCH_STACK_BYTES (offsetof(struct cpu_user_regs, es))
+#define CTXT_SWITCH_STACK_BYTES sizeof(struct cpu_user_regs)
 
 #define guest_mode(r)                                                         \
 ({                                                                            \
diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
index 34dc077cad..238d923dd1 100644
--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -387,7 +387,7 @@ unsigned long get_stack_trace_bottom(unsigned long sp)
     {
     case 1 ... 4:
         return ROUNDUP(sp, PAGE_SIZE) -
-            offsetof(struct cpu_user_regs, es) - sizeof(unsigned long);
+            sizeof(struct cpu_user_regs) - sizeof(unsigned long);
 
     case 6 ... 7:
         return ROUNDUP(sp, STACK_SIZE) -
diff --git a/xen/arch/x86/x86_64/asm-offsets.c 
b/xen/arch/x86/x86_64/asm-offsets.c
index 630bdc3945..2258b4ce1b 100644
--- a/xen/arch/x86/x86_64/asm-offsets.c
+++ b/xen/arch/x86/x86_64/asm-offsets.c
@@ -52,7 +52,7 @@ void __dummy__(void)
     OFFSET(UREGS_eflags, struct cpu_user_regs, rflags);
     OFFSET(UREGS_rsp, struct cpu_user_regs, rsp);
     OFFSET(UREGS_ss, struct cpu_user_regs, ss);
-    OFFSET(UREGS_kernel_sizeof, struct cpu_user_regs, es);
+    DEFINE(UREGS_kernel_sizeof, sizeof(struct cpu_user_regs));
     BLANK();
 
     /*
diff --git a/xen/arch/x86/x86_64/traps.c b/xen/arch/x86/x86_64/traps.c
index 29ac5a14ca..34adf55e48 100644
--- a/xen/arch/x86/x86_64/traps.c
+++ b/xen/arch/x86/x86_64/traps.c
@@ -135,17 +135,11 @@ static void _show_registers(
 
 void show_registers(const struct cpu_user_regs *regs)
 {
-    struct cpu_user_regs fault_regs;
+    struct cpu_user_regs fault_regs = *regs;
     struct extra_state fault_state;
     enum context context;
     struct vcpu *v = system_state >= SYS_STATE_smp_boot ? current : NULL;
 
-    /*
-     * Don't read beyond the end of the hardware frame.  It is out of bounds
-     * for WARN()/etc.
-     */
-    memcpy(&fault_regs, regs, offsetof(struct cpu_user_regs, es));
-
     if ( guest_mode(regs) && is_hvm_vcpu(v) )
     {
         get_hvm_registers(v, &fault_regs, &fault_state);
--
generated by git-patchbot for /home/xen/git/xen.git#master