Some kernel text swapping code

Makefile

@@ -84,7 +84,7 @@ INCLUDES := -include param.h -iquote libutil/include -I$(MTRACESRC)
 COMFLAGS := -pthread -Wno-unused-result
 LDFLAGS := -pthread
 endif
-COMFLAGS += -g -MD -MP -O3 -Wall -DHW_$(HW) $(INCLUDES) -fno-stack-protector
+COMFLAGS += -g -MD -MP -O3 -Wall -DHW_$(HW) $(INCLUDES) -fno-stack-protector # -mindirect-branch=thunk
 CFLAGS   := $(COMFLAGS) -std=c99 $(CFLAGS)
 CXXFLAGS := $(COMFLAGS) -std=c++17 -Wno-sign-compare -faligned-new $(CXXFLAGS)
 ASFLAGS  := $(ASFLAGS) -Iinclude -I$(O)/include -m64 -gdwarf-2 -MD -MP -DHW_$(HW) -include param.h

include/kernel.hh

@@ -119,6 +119,9 @@ int             futexkey(const u64* useraddr, vmap* vmap, futexkey_t* key);
 long            futexwait(futexkey_t key, u64 val, u64 timer);
 long            futexwake(futexkey_t key, u64 nwake);
 
+// hotpatch.cc
+extern void*    qtext;
+
 // hz.c
 void            microdelay(u64);
 void            inithz(void);

kernel/Makefrag

@@ -20,6 +20,7 @@ OBJS = \
         futex.o \
         idle.o \
 	ioapic.o \
+	hotpatch.o \
 	hwvm.o \
 	hz.o \
 	kalloc.o \

kernel/hotpatch.cc

@@ -0,0 +1,64 @@
+#include <string.h>
+#include "types.h"
+#include "kernel.hh"
+
+void* qtext;
+
+// extern u64 __x86_indirect_thunk_rax;
+// extern u64 __x86_indirect_thunk_rcx;
+// extern u64 __x86_indirect_thunk_rdx;
+// extern u64 __x86_indirect_thunk_rbx;
+// extern u64 __x86_indirect_thunk_rsi;
+// extern u64 __x86_indirect_thunk_r8;
+// extern u64 __x86_indirect_thunk_r9;
+// extern u64 __x86_indirect_thunk_r10;
+// extern u64 __x86_indirect_thunk_r12;
+// extern u64 __x86_indirect_thunk_r13;
+// extern u64 __x86_indirect_thunk_r14;
+// extern u64 __x86_indirect_thunk_r15;
+
+// void* retpoline_thunks[] = {
+//     (void*)&__x86_indirect_thunk_rax,
+//     (void*)&__x86_indirect_thunk_rcx,
+//     (void*)&__x86_indirect_thunk_rdx,
+//     (void*)&__x86_indirect_thunk_rbx,
+//     (void*)&__x86_indirect_thunk_rsi,
+//     (void*)&__x86_indirect_thunk_r8,
+//     (void*)&__x86_indirect_thunk_r9,
+//     (void*)&__x86_indirect_thunk_r10,
+//     (void*)&__x86_indirect_thunk_r12,
+//     (void*)&__x86_indirect_thunk_r13,
+// };
+
+// void* text_to_qtext(void* addr) {
+//   return (char*)addr - KCODE + (u64)qtext;
+// }
+
+// void replace_qtext_u16(void* target, u16 value) {
+//     *(u16*)text_to_qtext(target) = value;
+// }
+// void replace_qtext_u32(void* target, u32 value) {
+//     *(u32*)text_to_qtext(target) = value;
+// }
+
+// void remove_retpolines()
+// {
+//     replace_qtext_u16(&__x86_indirect_thunk_rax, 0xE0FF);
+//     replace_qtext_u16(&__x86_indirect_thunk_rcx, 0xE1FF);
+//     replace_qtext_u16(&__x86_indirect_thunk_rdx, 0xE2FF);
+//     replace_qtext_u16(&__x86_indirect_thunk_rbx, 0xE3FF);
+//     replace_qtext_u16(&__x86_indirect_thunk_rsi, 0xE6FF);
+//     replace_qtext_u32(&__x86_indirect_thunk_r8, 0xE0FF41);
+//     replace_qtext_u32(&__x86_indirect_thunk_r9, 0xE1FF41);
+//     replace_qtext_u32(&__x86_indirect_thunk_r10, 0xE2FF41);
+//     replace_qtext_u32(&__x86_indirect_thunk_r12, 0xE4FF41);
+//     replace_qtext_u32(&__x86_indirect_thunk_r13, 0xE5FF41);
+// }
+
+void inithotpatch()
+{
+    qtext = kalloc("qtext", 0x200000);
+    memset(qtext, 0, 0x100000);
+    memmove(qtext + 0x100000, (void*)KCODE + 0x100000, 0x100000);
+    // remove_retpolines();
+}

kernel/hwvm.cc

@@ -132,7 +132,6 @@ struct pgmap {
 
     k = PX(L_PML4, KGLOBAL);
     memset(&pair.user->e[0], 0, PGSIZE);
-    pair.user->uexpose((void*)KCODE, L_2M, true);
 
     return pair;
   }
@@ -698,6 +697,7 @@ namespace mmu_per_core_page_table {
         mypml4s.user->uexpose((void*)(mycpu()->ts.ist[1] + i - KSTACKSIZE), pgmap::L_4K); // nmi stack
         mypml4s.user->uexpose((void*)(mycpu()->ts.ist[2] + i - KSTACKSIZE), pgmap::L_4K); // double fault stack
       }
+      *(mypml4s.user->find(KCODE, pgmap::L_2M).create(0)) = v2p(qtext) | PTE_PS | PTE_P | PTE_W;
     }
 
     // TODO(behrensj): Avoid doing this on every `switch_to` call.

kernel/main.cc

@@ -62,6 +62,7 @@ void inithpet(void);
 void initrtc(void);
 void initmfs(void);
 void idleloop(void);
+void inithotpatch(void);
 
 #define IO_RTC  0x70
 
@@ -246,6 +247,7 @@ cmain(u64 mbmagic, u64 mbaddr)
   initdisk();      // disk
   initinode();     // inode cache
   initmfs();
+  inithotpatch();
 
   if (VERBOSE)
     cprintf("ncpu %d %lu MHz\n", ncpu, cpuhz / 1000000);

net/Makefrag

@@ -21,7 +21,7 @@ LWIP_CFLAGS = -Wno-attributes \
 	    -Wno-char-subscripts \
 	    -Wno-unused-but-set-variable \
 	    -Wno-format \
-	    -mcmodel=large -O2
+	    -mcmodel=kernel -O2 -mindirect-branch=keep
 
 LWIP_INCLUDES := \
 	-Ilwip/src/include \
@@ -62,8 +62,8 @@ LWIP_SRCFILES += \
 	net/if.c
 LWIP_OBJFILES := $(patsubst %.c, $(O)/%.o, $(LWIP_SRCFILES))
 
-$(O)/net/%.o: CXXFLAGS+=-mcmodel=large -DXV6_KERNEL
-$(O)/lwip/src/%.o: CFLAGS+=-mcmodel=large $(LWIP_CFLAGS) $(LWIP_INCLUDES)
+$(O)/net/%.o: CXXFLAGS+=-mcmodel=kernel -DXV6_KERNEL
+$(O)/lwip/src/%.o: CFLAGS+=-mcmodel=kernel $(LWIP_CFLAGS) $(LWIP_INCLUDES)
 
 $(O)/liblwip.a: $(LWIP_OBJFILES)
 	@echo "  AR     $@"