From f46ab8ca2050ee77edf6e6b979875426bdaf29dc Mon Sep 17 00:00:00 2001
From: Jon Santmyer <jon@jonsantmyer.com>
Date: Wed, 13 Mar 2024 09:58:22 -0400
Subject: fix incorrect tss rsp assignment

---
 arch/x86_64/gdt.c | 42 +++++++++++++++++++++++++++++-------------
 1 file changed, 29 insertions(+), 13 deletions(-)

(limited to 'arch/x86_64/gdt.c')

diff --git a/arch/x86_64/gdt.c b/arch/x86_64/gdt.c
index d996dcb..07a8097 100644
--- a/arch/x86_64/gdt.c
+++ b/arch/x86_64/gdt.c
@@ -25,14 +25,15 @@ static struct SegmentDescriptor s_gdtd[GDT_SEGMENT_COUNT] =
         .limit_0_15 = 0xFFFF,
         .base_0_15 = 0,
         .base_16_23 = 0,
-        .type = CD_SEGMENT_TYPE_CODE | CD_SEGMENT_TYPE_CODE_CONFORMING,
+        .type = CD_SEGMENT_TYPE_CODE | CD_SEGMENT_TYPE_WRITEABLE,
         .s = 1,
         .dpl = 0,
         .p = 1,
         .limit_16_19 = 0xF,
+        .avl = 0,
         .l = 1,
         .d_b = 0,
-        .g = 0,
+        .g = 1,
         .base_24_31 = 0
     },
     {       /* Kernel Data (64-bit RW DPL0) */
@@ -44,9 +45,10 @@ static struct SegmentDescriptor s_gdtd[GDT_SEGMENT_COUNT] =
         .dpl = 0,
         .p = 1,
         .limit_16_19 = 0xF,
-        .l = 1,
-        .d_b = 0,
-        .g = 0,
+        .avl = 0,
+        .l = 0,
+        .d_b = 1,
+        .g = 1,
         .base_24_31 = 0
     },
     { 0 },  /* User NULL */
@@ -59,36 +61,38 @@ static struct SegmentDescriptor s_gdtd[GDT_SEGMENT_COUNT] =
         .dpl = 3,
         .p = 1,
         .limit_16_19 = 0xF,
-        .l = 1,
-        .d_b = 0,
-        .g = 0,
+        .avl = 0,
+        .l = 0,
+        .d_b = 1,
+        .g = 1,
         .base_24_31 = 0,
     },
     {       /* User Code (64-bit RO EX DPL3)*/
         .limit_0_15 = 0xFFFF,
         .base_0_15 = 0,
         .base_16_23 = 0,
-        .type = CD_SEGMENT_TYPE_CODE | CD_SEGMENT_TYPE_CODE_CONFORMING,
+        .type = CD_SEGMENT_TYPE_CODE | CD_SEGMENT_TYPE_WRITEABLE,
         .s = 1,
         .dpl = 3,
         .p = 1,
         .limit_16_19 = 0xF,
+        .avl = 0,
         .l = 1,
         .d_b = 0,
-        .g = 0,
+        .g = 1,
         .base_24_31 = 0,
     },
     {       /* TSS Low */
-        .limit_0_15 = sizeof(struct TSS),
+        .limit_0_15 = 0,
         .base_0_15 = 0,
         .base_16_23 = 0,
         .type = S_SEGMENT_TYPE_TSS_AVAIL,
-        .avl = 1,
+        .avl = 0,
         .s = 0,
         .dpl = 0,
         .p = 1,
         .limit_16_19 = 0,
-        .l = 1,
+        .l = 0,
         .d_b = 0,
         .g = 0,
         .base_24_31 = 0,
@@ -118,8 +122,20 @@ x86_64_load_gdt(void)
         tss_lo->base_24_31 = (tssb >> 24) & 0xFF;
         tss_hi->limit_0_15 = (tssb >> 32) & 0xFFFF;
         tss_hi->base_0_15 = (tssb >> 48) & 0xFFFF;
+
+        size_t tssl = sizeof(struct TSS) - 1;
+        tss_lo->limit_0_15 = tssl & 0xFFFF;
+        tss_lo->limit_16_19 = (tssl >> 16) & 0xF;
+
+        s_tss.iobp = sizeof(struct TSS);
     }
 
     x86_64_lgdt(&s_gdtr);
     x86_64_flush_tss();
 }
+
+void tss_set_rsp(uint8_t dpl, uintptr_t rsp)
+{
+    s_tss.rsp[dpl][0] = rsp & 0xFFFFFFFF;
+    s_tss.rsp[dpl][1] = (rsp >> 32) & 0xFFFFFFFF;
+}
-- 
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