[PATCH 07/10] target/i386/tcg: Use DPL-level accesses for interrupts and call gates

[Paolo Bonzini]

This fixes a bug wherein i386/tcg assumed an interrupt return using
the CALL or JMP instructions were always going from kernel or user mode to
kernel mode, when using a call gate. This assumption is violated if
the call gate has a DPL that is greater than 0.

In addition, the stack accesses should count as explicit, not implicit
("kernel" in QEMU code), so that SMAP is not applied if DPL=3.

Analyzed-by: Robert R. Henry <rrh.henry@gmail.com>
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/249
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 target/i386/tcg/seg_helper.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/target/i386/tcg/seg_helper.c b/target/i386/tcg/seg_helper.c
index 07e3667639a..1430f477c43 100644
--- a/target/i386/tcg/seg_helper.c
+++ b/target/i386/tcg/seg_helper.c
@@ -678,7 +678,7 @@ static void do_interrupt_protected(CPUX86State *env, int 
intno, int is_int,
 
     sa.env = env;
     sa.ra = 0;
-    sa.mmu_index = cpu_mmu_index_kernel(env);
+    sa.mmu_index = x86_mmu_index_pl(env, dpl);
 
     if (type == 5) {
         /* task gate */
@@ -984,7 +984,7 @@ static void do_interrupt64(CPUX86State *env, int intno, int 
is_int,
 
     sa.env = env;
     sa.ra = 0;
-    sa.mmu_index = cpu_mmu_index_kernel(env);
+    sa.mmu_index = x86_mmu_index_pl(env, dpl);
     sa.sp_mask = -1;
     sa.ss_base = 0;
     if (dpl < cpl || ist != 0) {
@@ -1119,7 +1119,7 @@ static void do_interrupt_real(CPUX86State *env, int 
intno, int is_int,
     sa.sp = env->regs[R_ESP];
     sa.sp_mask = 0xffff;
     sa.ss_base = env->segs[R_SS].base;
-    sa.mmu_index = cpu_mmu_index_kernel(env);
+    sa.mmu_index = x86_mmu_index_pl(env, 0);
 
     if (is_int) {
         old_eip = next_eip;
@@ -1583,7 +1583,7 @@ void helper_lcall_real(CPUX86State *env, uint32_t new_cs, 
uint32_t new_eip,
     sa.sp = env->regs[R_ESP];
     sa.sp_mask = get_sp_mask(env->segs[R_SS].flags);
     sa.ss_base = env->segs[R_SS].base;
-    sa.mmu_index = cpu_mmu_index_kernel(env);
+    sa.mmu_index = x86_mmu_index_pl(env, 0);
 
     if (shift) {
         pushl(&sa, env->segs[R_CS].selector);
@@ -1619,17 +1619,17 @@ void helper_lcall_protected(CPUX86State *env, int 
new_cs, target_ulong new_eip,
         raise_exception_err_ra(env, EXCP0D_GPF, new_cs & 0xfffc, GETPC());
     }
     cpl = env->hflags & HF_CPL_MASK;
+    dpl = (e2 >> DESC_DPL_SHIFT) & 3;
     LOG_PCALL("desc=%08x:%08x\n", e1, e2);
 
     sa.env = env;
     sa.ra = GETPC();
-    sa.mmu_index = cpu_mmu_index_kernel(env);
+    sa.mmu_index = x86_mmu_index_pl(env, dpl);
 
     if (e2 & DESC_S_MASK) {
         if (!(e2 & DESC_CS_MASK)) {
             raise_exception_err_ra(env, EXCP0D_GPF, new_cs & 0xfffc, GETPC());
         }
-        dpl = (e2 >> DESC_DPL_SHIFT) & 3;
         if (e2 & DESC_C_MASK) {
             /* conforming code segment */
             if (dpl > cpl) {
@@ -1691,7 +1691,6 @@ void helper_lcall_protected(CPUX86State *env, int new_cs, 
target_ulong new_eip,
     } else {
         /* check gate type */
         type = (e2 >> DESC_TYPE_SHIFT) & 0x1f;
-        dpl = (e2 >> DESC_DPL_SHIFT) & 3;
         rpl = new_cs & 3;
 
 #ifdef TARGET_X86_64
-- 
2.45.2