Add usermode util that enables running a function in user mode.
In addition, it enables catching an exception which is raised from
the user-mode function.
Signed-off-by: Arbel Moshe <arbel.moshe@xxxxxxxxxx>
Reviewed-by: Liran Alon <liran.alon@xxxxxxxxxx>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
---
lib/x86/usermode.c | 113 ++++++++++++++++++++++++++++++++++++++++++++++++++++
lib/x86/usermode.h | 30 ++++++++++++++
x86/Makefile.common | 1 +
3 files changed, 144 insertions(+)
create mode 100644 lib/x86/usermode.c
create mode 100644 lib/x86/usermode.h
diff --git a/lib/x86/usermode.c b/lib/x86/usermode.c
new file mode 100644
index 0000000..323d84d
--- /dev/null
+++ b/lib/x86/usermode.c
@@ -0,0 +1,113 @@
+#include "x86/msr.h"
+#include "x86/processor.h"
+#include "x86/apic-defs.h"
+#include "x86/apic.h"
+#include "x86/desc.h"
+#include "x86/isr.h"
+#include "alloc.h"
+#include "setjmp.h"
+#include "usermode.h"
+
+#include "libcflat.h"
+#include <stdint.h>
+
+#define USERMODE_STACK_SIZE 0x2000
+#define RET_TO_KERNEL_IRQ 0x20
+
+jmp_buf jmpbuf;
+
+static void restore_exec_to_jmpbuf(void)
+{
+ longjmp(jmpbuf, 1);
+}
+
+static void restore_exec_to_jmpbuf_exception_handler(struct ex_regs *regs)
+{
+ /* longjmp must happen after iret, so do not do it now. */
+ regs->rip = (unsigned long)&restore_exec_to_jmpbuf;
+ regs->cs = KERNEL_CS;
+}
+
+uint64_t run_in_user(usermode_func func, unsigned int fault_vector,
+ uint64_t arg1, uint64_t arg2, uint64_t arg3,
+ uint64_t arg4, bool *raised_vector)
+{
+ extern char ret_to_kernel;
+ uint64_t rax = 0;
+ static unsigned char user_stack[USERMODE_STACK_SIZE];
+
+ *raised_vector = 0;
+ set_idt_entry(RET_TO_KERNEL_IRQ, &ret_to_kernel, 3);
+ handle_exception(fault_vector,
+ restore_exec_to_jmpbuf_exception_handler);
+
+ if (setjmp(jmpbuf) != 0) {
+ *raised_vector = 1;
+ return 0;
+ }
+
+ asm volatile (
+ /* Backing Up Stack in rdi */
+ "mov %%rsp, %%rdi\n\t"
+ /* Load user_ds to DS and ES */
+ "mov %[user_ds], %%ax\n\t"
+ "mov %%ax, %%ds\n\t"
+ "mov %%ax, %%es\n\t"
+ /* IRET into user mode */
+ "pushq %[user_ds]\n\t"
+ "pushq %[user_stack_top]\n\t"
+ "pushfq\n\t"
+ "pushq %[user_cs]\n\t"
+ "pushq $user_mode\n\t"
+ "iretq\n"
+
+ "user_mode:\n\t"
+ /* Back up registers before invoking func */
+ "push %%rbx\n\t"
+ "push %%rcx\n\t"
+ "push %%rdx\n\t"
+ "push %%r8\n\t"
+ "push %%r9\n\t"
+ "push %%r10\n\t"
+ "push %%r11\n\t"
+ "push %%rdi\n\t"
+ "push %%rsi\n\t"
+ /* Call user mode function */
+ "mov %[arg1], %%rdi\n\t"
+ "mov %[arg2], %%rsi\n\t"
+ "mov %[arg3], %%rdx\n\t"
+ "mov %[arg4], %%rcx\n\t"
+ "call %[func]\n\t"
+ /* Restore registers */
+ "pop %%rsi\n\t"
+ "pop %%rdi\n\t"
+ "pop %%r11\n\t"
+ "pop %%r10\n\t"
+ "pop %%r9\n\t"
+ "pop %%r8\n\t"
+ "pop %%rdx\n\t"
+ "pop %%rcx\n\t"
+ "pop %%rbx\n\t"
+ /* Return to kernel via system call */
+ "int %[kernel_entry_vector]\n\t"
+ /* Kernel Mode */
+ "ret_to_kernel:\n\t"
+ "mov %%rdi, %%rsp\n\t"
+ :
+ "+a"(rax)
+ :
+ [arg1]"m"(arg1),
+ [arg2]"m"(arg2),
+ [arg3]"m"(arg3),
+ [arg4]"m"(arg4),
+ [func]"m"(func),
+ [user_ds]"i"(USER_DS),
+ [user_cs]"i"(USER_CS),
+ [user_stack_top]"r"(user_stack +
+ sizeof(user_stack)),
+ [kernel_entry_vector]"i"(RET_TO_KERNEL_IRQ)
+ :
+ "rsi", "rdi", "rcx", "rdx");
+
+ return rax;
+}
diff --git a/lib/x86/usermode.h b/lib/x86/usermode.h
new file mode 100644
index 0000000..4e005e6
--- /dev/null
+++ b/lib/x86/usermode.h
@@ -0,0 +1,30 @@
+#ifndef _USERMODE_H_
+#define _USERMODE_H_
+
+#include "x86/msr.h"
+#include "x86/processor.h"
+#include "x86/apic-defs.h"
+#include "x86/apic.h"
+#include "x86/desc.h"
+#include "x86/isr.h"
+#include "alloc.h"
+#include "setjmp.h"
+
+#include "libcflat.h"
+#include <stdint.h>
+
+typedef uint64_t (*usermode_func)(void);
+
+/*
+ * Run function in user mode
+ * Supports running functions with up to 4 arguments.
+ * fault_vector: exception vector that might get thrown during the function.
+ * raised_vector: outputs true if exception occurred.
+ *
+ * returns: return value returned by function, or 0 if an exception occurred.
+ */
+uint64_t run_in_user(usermode_func func, unsigned int fault_vector,
+ uint64_t arg1, uint64_t arg2, uint64_t arg3,
+ uint64_t arg4, bool *raised_vector);
+
+#endif
diff --git a/x86/Makefile.common b/x86/Makefile.common
index 5f7eac4..8a9d245 100644
--- a/x86/Makefile.common
+++ b/x86/Makefile.common
@@ -19,6 +19,7 @@ cflatobjs += lib/x86/desc.o
cflatobjs += lib/x86/isr.o
cflatobjs += lib/x86/acpi.o
cflatobjs += lib/x86/stack.o
+cflatobjs += lib/x86/usermode.o
OBJDIRS += lib/x86
--
2.14.1
