hvm: Register fields CS,DS,ES,FS,GS,SS,etc. are all undefined during

HVM execution as they are not saved/restore on vmexit/vmentry. To
prevent accidental usage of these fields, poison them with 16-bit
value 0xbeef (debug builds only).
Signed-off-by: Keir Fraser <keir.fraser@citrix.com>

6 files changed, 58 insertions, 1 deletions

diff --git a/xen/arch/x86/hvm/svm/x86_32/exits.S b/xen/arch/x86/hvm/svm/x86_32/exits.S
index f9c29a6d95..83d893a90d 100644
--- a/xen/arch/x86/hvm/svm/x86_32/exits.S
+++ b/xen/arch/x86/hvm/svm/x86_32/exits.S
@@ -94,6 +94,19 @@ svm_trace_done:
         movl VMCB_rflags(%ecx),%eax
         movl %eax,UREGS_eflags(%esp)
 
+#ifndef NDEBUG
+        movw $0xbeef,%ax
+        movw %ax,UREGS_error_code(%esp)
+        movw %ax,UREGS_entry_vector(%esp)
+        movw %ax,UREGS_saved_upcall_mask(%esp)
+        movw %ax,UREGS_cs(%esp)
+        movw %ax,UREGS_ds(%esp)
+        movw %ax,UREGS_es(%esp)
+        movw %ax,UREGS_fs(%esp)
+        movw %ax,UREGS_gs(%esp)
+        movw %ax,UREGS_ss(%esp)
+#endif
+
         STGI
 .globl svm_stgi_label;
 svm_stgi_label:
diff --git a/xen/arch/x86/hvm/svm/x86_64/exits.S b/xen/arch/x86/hvm/svm/x86_64/exits.S
index 99ffea4a8f..8c2f70a6bd 100644
--- a/xen/arch/x86/hvm/svm/x86_64/exits.S
+++ b/xen/arch/x86/hvm/svm/x86_64/exits.S
@@ -113,6 +113,19 @@ svm_trace_done:
         movq VMCB_rflags(%rcx),%rax
         movq %rax,UREGS_eflags(%rsp)
 
+#ifndef NDEBUG
+        movw $0xbeef,%ax
+        movw %ax,UREGS_error_code(%rsp)
+        movw %ax,UREGS_entry_vector(%rsp)
+        movw %ax,UREGS_saved_upcall_mask(%rsp)
+        movw %ax,UREGS_cs(%rsp)
+        movw %ax,UREGS_ds(%rsp)
+        movw %ax,UREGS_es(%rsp)
+        movw %ax,UREGS_fs(%rsp)
+        movw %ax,UREGS_gs(%rsp)
+        movw %ax,UREGS_ss(%rsp)
+#endif
+
         STGI
 .globl svm_stgi_label;
 svm_stgi_label:
diff --git a/xen/arch/x86/hvm/vmx/x86_32/exits.S b/xen/arch/x86/hvm/vmx/x86_32/exits.S
index ff0cd6f43c..09202eaed3 100644
--- a/xen/arch/x86/hvm/vmx/x86_32/exits.S
+++ b/xen/arch/x86/hvm/vmx/x86_32/exits.S
@@ -40,7 +40,6 @@
         movl (reg),reg;
 
 #define HVM_SAVE_ALL_NOSEGREGS                                              \
-        movl $0, 0xc(%esp);  /* XXX why do we need to force eflags==0 ?? */ \
         pushl %eax;                                                         \
         pushl %ebp;                                                         \
         pushl %edi;                                                         \
@@ -69,6 +68,19 @@ ENTRY(vmx_asm_vmexit_handler)
         movl $GUEST_RFLAGS,%eax
         VMREAD(UREGS_eflags)
 
+#ifndef NDEBUG
+        movw $0xbeef,%ax
+        movw %ax,UREGS_error_code(%esp)
+        movw %ax,UREGS_entry_vector(%esp)
+        movw %ax,UREGS_saved_upcall_mask(%esp)
+        movw %ax,UREGS_cs(%esp)
+        movw %ax,UREGS_ds(%esp)
+        movw %ax,UREGS_es(%esp)
+        movw %ax,UREGS_fs(%esp)
+        movw %ax,UREGS_gs(%esp)
+        movw %ax,UREGS_ss(%esp)
+#endif
+
         movl %esp,%eax
         push %eax
         call vmx_vmexit_handler
diff --git a/xen/arch/x86/hvm/vmx/x86_64/exits.S b/xen/arch/x86/hvm/vmx/x86_64/exits.S
index a54d7ef79c..0adb337681 100644
--- a/xen/arch/x86/hvm/vmx/x86_64/exits.S
+++ b/xen/arch/x86/hvm/vmx/x86_64/exits.S
@@ -86,6 +86,19 @@ ENTRY(vmx_asm_vmexit_handler)
         movl $GUEST_RFLAGS,%eax
         VMREAD(UREGS_eflags)
 
+#ifndef NDEBUG
+        movw $0xbeef,%ax
+        movw %ax,UREGS_error_code(%rsp)
+        movw %ax,UREGS_entry_vector(%rsp)
+        movw %ax,UREGS_saved_upcall_mask(%rsp)
+        movw %ax,UREGS_cs(%rsp)
+        movw %ax,UREGS_ds(%rsp)
+        movw %ax,UREGS_es(%rsp)
+        movw %ax,UREGS_fs(%rsp)
+        movw %ax,UREGS_gs(%rsp)
+        movw %ax,UREGS_ss(%rsp)
+#endif
+
         movq %rsp,%rdi
         call vmx_vmexit_handler
         jmp vmx_asm_do_vmentry
diff --git a/xen/arch/x86/x86_32/asm-offsets.c b/xen/arch/x86/x86_32/asm-offsets.c
index 17beecc759..2e08ccf2fd 100644
--- a/xen/arch/x86/x86_32/asm-offsets.c
+++ b/xen/arch/x86/x86_32/asm-offsets.c
@@ -44,6 +44,7 @@ void __dummy__(void)
     OFFSET(UREGS_eflags, struct cpu_user_regs, eflags);
     OFFSET(UREGS_error_code, struct cpu_user_regs, error_code);
     OFFSET(UREGS_entry_vector, struct cpu_user_regs, entry_vector);
+    OFFSET(UREGS_saved_upcall_mask, struct cpu_user_regs, saved_upcall_mask);
     OFFSET(UREGS_kernel_sizeof, struct cpu_user_regs, esp);
     DEFINE(UREGS_user_sizeof, sizeof(struct cpu_user_regs));
     BLANK();
diff --git a/xen/arch/x86/x86_64/asm-offsets.c b/xen/arch/x86/x86_64/asm-offsets.c
index ce92b848c9..8a7c55f951 100644
--- a/xen/arch/x86/x86_64/asm-offsets.c
+++ b/xen/arch/x86/x86_64/asm-offsets.c
@@ -46,11 +46,16 @@ void __dummy__(void)
     OFFSET(UREGS_rdi, struct cpu_user_regs, rdi);
     OFFSET(UREGS_error_code, struct cpu_user_regs, error_code);
     OFFSET(UREGS_entry_vector, struct cpu_user_regs, entry_vector);
+    OFFSET(UREGS_saved_upcall_mask, struct cpu_user_regs, saved_upcall_mask);
     OFFSET(UREGS_rip, struct cpu_user_regs, rip);
     OFFSET(UREGS_cs, struct cpu_user_regs, cs);
     OFFSET(UREGS_eflags, struct cpu_user_regs, eflags);
     OFFSET(UREGS_rsp, struct cpu_user_regs, rsp);
     OFFSET(UREGS_ss, struct cpu_user_regs, ss);
+    OFFSET(UREGS_ds, struct cpu_user_regs, ds);
+    OFFSET(UREGS_es, struct cpu_user_regs, es);
+    OFFSET(UREGS_fs, struct cpu_user_regs, fs);
+    OFFSET(UREGS_gs, struct cpu_user_regs, gs);
     OFFSET(UREGS_kernel_sizeof, struct cpu_user_regs, es);
     DEFINE(UREGS_user_sizeof, sizeof(struct cpu_user_regs));
     BLANK();