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[Qemu-devel] [PATCH 1/5] kqemu: x86-64: Run 16-bit-stack-return in ring


From: Jan Kiszka
Subject: [Qemu-devel] [PATCH 1/5] kqemu: x86-64: Run 16-bit-stack-return in ring 0
Date: Fri, 29 May 2009 19:18:31 +0200
User-agent: StGIT/0.14.3

The fix-up code for returning to 16 bit stack segments is currently
executed in ring 1. This has the side effect that the interrupt flag
remains cleared on return from ring 1 to the guest's ring 3 as its
IOPL is 0 (ie. iret can only modify IF when run in ring 0).

Fix this by moving the 32 bit return trampoline into ring 0.

Signed-off-by: Jan Kiszka <address@hidden>
---

 common/kernel.c |    8 ++++----
 1 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/common/kernel.c b/common/kernel.c
index 6a88452..1d7a69e 100644
--- a/common/kernel.c
+++ b/common/kernel.c
@@ -422,8 +422,8 @@ struct kqemu_state *kqemu_init(struct kqemu_init *d,
 #ifdef __x86_64__
     s->monitor_ds_sel = 0; /* no need for a specific data segment */
     /* used for 16 bit esp fix */
-    s->monitor_cs32_sel = (s->monitor_selector_base + (7 << 3)) | 1;
-    s->monitor_ss16_sel = (s->monitor_selector_base + (6 << 3)) | 1;
+    s->monitor_cs32_sel = s->monitor_selector_base + (7 << 3);
+    s->monitor_ss16_sel = s->monitor_selector_base + (6 << 3);
     s->monitor_ss_null_sel = (s->monitor_selector_base + (1 << 3)) | 3;
 #else
     s->monitor_ds_sel = s->monitor_selector_base + (1 << 3);
@@ -495,9 +495,9 @@ struct kqemu_state *kqemu_init(struct kqemu_init *d,
                 0, 0xfffff, 0xa09a); /* long mode segment */
         set_seg((uint32_t *)(dt_table + (s->monitor_ss16_sel >> 3)),
                 (s->monitor_data_vaddr + offsetof(struct kqemu_state, stack)) 
& ~0xffff, 
-                0xffff, 0x00b2); /* SS16 segment for 16 bit ESP fix */
+                0xffff, 0x0092); /* SS16 segment for 16 bit ESP fix */
         set_seg((uint32_t *)(dt_table + (s->monitor_cs32_sel >> 3)),
-                0, 0xfffff, 0xc0ba); /* CS32 segment for 16 bit ESP fix */
+                0, 0xfffff, 0xc09a); /* CS32 segment for 16 bit ESP fix */
         set_seg((uint32_t *)(dt_table + (s->monitor_ss_null_sel >> 3)),
                 0, 0, 0x40f2); /* substitute for null SS segment */
 #else





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