[Qemu-devel] [PATCH 2/3] target-i386: rework CPL checks during task switch, preparing for next patch

[Paolo Bonzini <pbonzini@redhat.com>]

During task switch, all of CS.DPL, CS.RPL, SS.DPL must match (in addition
to all the other requirements) and will be the new CPL.  So far this worked
by carefully setting the CS selector and flags before doing the task
switch; but this will not work once we get the CPL from SS.DPL.

Temporarily assume that the CPL comes from CS.RPL during task switch
to a protected-mode task, until the descriptor of SS is loaded.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 target-i386/seg_helper.c | 23 +++++++++--------------
 1 file changed, 9 insertions(+), 14 deletions(-)

diff --git a/target-i386/seg_helper.c b/target-i386/seg_helper.c
index dd2c8b4..426b9c6 100644
--- a/target-i386/seg_helper.c
+++ b/target-i386/seg_helper.c
@@ -135,11 +135,10 @@ static inline void get_ss_esp_from_tss(CPUX86State *env, uint32_t *ss_ptr,
     }
 }
 
-/* XXX: merge with load_seg() */
-static void tss_load_seg(CPUX86State *env, int seg_reg, int selector)
+static void tss_load_seg(CPUX86State *env, int seg_reg, int selector, int cpl)
 {
     uint32_t e1, e2;
-    int rpl, dpl, cpl;
+    int rpl, dpl;
 
     if ((selector & 0xfffc) != 0) {
         if (load_segment(env, &e1, &e2, selector) != 0) {
@@ -150,18 +149,13 @@ static void tss_load_seg(CPUX86State *env, int seg_reg, int selector)
         }
         rpl = selector & 3;
         dpl = (e2 >> DESC_DPL_SHIFT) & 3;
-        cpl = env->hflags & HF_CPL_MASK;
         if (seg_reg == R_CS) {
             if (!(e2 & DESC_CS_MASK)) {
                 raise_exception_err(env, EXCP0A_TSS, selector & 0xfffc);
             }
-            /* XXX: is it correct? */
             if (dpl != rpl) {
                 raise_exception_err(env, EXCP0A_TSS, selector & 0xfffc);
             }
-            if ((e2 & DESC_C_MASK) && dpl > rpl) {
-                raise_exception_err(env, EXCP0A_TSS, selector & 0xfffc);
-            }
         } else if (seg_reg == R_SS) {
             /* SS must be writable data */
             if ((e2 & DESC_CS_MASK) || !(e2 & DESC_W_MASK)) {
@@ -448,12 +442,13 @@ static void switch_tss(CPUX86State *env, int tss_selector,
 
     /* load the segments */
     if (!(new_eflags & VM_MASK)) {
-        tss_load_seg(env, R_CS, new_segs[R_CS]);
-        tss_load_seg(env, R_SS, new_segs[R_SS]);
-        tss_load_seg(env, R_ES, new_segs[R_ES]);
-        tss_load_seg(env, R_DS, new_segs[R_DS]);
-        tss_load_seg(env, R_FS, new_segs[R_FS]);
-        tss_load_seg(env, R_GS, new_segs[R_GS]);
+        int cpl = new_segs[R_CS] & 3;
+        tss_load_seg(env, R_CS, new_segs[R_CS], cpl);
+        tss_load_seg(env, R_SS, new_segs[R_SS], cpl);
+        tss_load_seg(env, R_ES, new_segs[R_ES], cpl);
+        tss_load_seg(env, R_DS, new_segs[R_DS], cpl);
+        tss_load_seg(env, R_FS, new_segs[R_FS], cpl);
+        tss_load_seg(env, R_GS, new_segs[R_GS], cpl);
     }
 
     /* check that env->eip is in the CS segment limits */
-- 
1.8.3.1