[PATCH] UML - add elf vsyscall support
From: Jeff Dike
Date: Fri Dec 03 2004 - 14:30:55 EST
>From Bodo Stroesser:
This is the first patch of a series of four.
These patches allow the use of sysenter-systemcalls in UML
if the host support sysenter.
Some facts have to be noted:
- the sysenter instruction does not save anything, not even the
return address. Thus the host-kernel builds a stackframe with an
fixed return address for the backjump to the vsyscall-page. All
kernels that support sysenter thus must have a vsyscall-page
- The hosts vsyscall-page is visible in all memory-contexts on the
host, even in those of the processes running on UML. This cannot
be changed.
So the best way to implement sysenter is to integrate the host's
vsyscall-page into UML, if available.
This patch creates a new source file containing an UML
initialization function. The function scans the Elf-auxiliary vector
that is prepared by the host for relevant information about:
- vsyscall elf-header
- vsyscall entry
- machine type (called "platform", e.g. "i586" or "i686")
- hardware capabilities
These informations are inserted into the Elf-auxiliary-vector that is
generated if an UML process calls "execXX()". If the information from
the auxiliray-vector is not complete, UML uses the previos default
values, with one exception: if the host has no vsyscall-page, UML now
does no longer insert AT_SYSINFO or AT_SYSINFO_EHDR elements. (I think,
that's better than writing dummies)
Since the host's vsyscall-page is always visible to UML processes, this
change is enough to let UML with an i686-compiled glibc use sysenter.
what's missing:
- is_syscall() in SKAS cannot access the code in the vsyscall-page via
copy_from_user(), thus singlesteppers still could break out. (Note:
that's not new, if someone jumps willingly to the sysenter-entry in
the vsyscall-page, he can do that without the patch, too).
- a debugger cannot access the code in the vsyscall-page via
ptrace( PEEKTEXT, ...)
Risks:
could there by any feature of the host's processor, that is indicated in
the hardware capabilities, but must not be used in UML?
Signed-off-by: Bodo Stroesser <bodo.stroesser@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Jeff Dike <jdike@xxxxxxxxxxx>
Index: 2.6.9/arch/um/kernel/main.c
===================================================================
--- 2.6.9.orig/arch/um/kernel/main.c 2004-12-01 23:43:04.000000000 -0500
+++ 2.6.9/arch/um/kernel/main.c 2004-12-01 23:44:11.000000000 -0500
@@ -81,6 +81,8 @@
extern int uml_exitcode;
+extern void scan_elf_aux( char **envp);
+
int main(int argc, char **argv, char **envp)
{
char **new_argv;
@@ -147,6 +149,8 @@
set_handler(SIGTERM, last_ditch_exit, SA_ONESHOT | SA_NODEFER, -1);
set_handler(SIGHUP, last_ditch_exit, SA_ONESHOT | SA_NODEFER, -1);
+ scan_elf_aux( envp);
+
do_uml_initcalls();
ret = linux_main(argc, argv);
Index: 2.6.9/arch/um/kernel/um_arch.c
===================================================================
--- 2.6.9.orig/arch/um/kernel/um_arch.c 2004-12-01 23:43:04.000000000 -0500
+++ 2.6.9/arch/um/kernel/um_arch.c 2004-12-01 23:44:11.000000000 -0500
@@ -44,11 +44,6 @@
.ipi_pipe = { -1, -1 }
};
-/* Placeholder to make UML link until the vsyscall stuff is actually
- * implemented
- */
-void *__kernel_vsyscall;
-
unsigned long thread_saved_pc(struct task_struct *task)
{
return(os_process_pc(CHOOSE_MODE_PROC(thread_pid_tt, thread_pid_skas,
Index: 2.6.9/arch/um/os-Linux/Makefile
===================================================================
--- 2.6.9.orig/arch/um/os-Linux/Makefile 2004-12-01 23:43:12.000000000 -0500
+++ 2.6.9/arch/um/os-Linux/Makefile 2004-12-01 23:45:55.000000000 -0500
@@ -3,9 +3,10 @@
# Licensed under the GPL
#
-obj-y = file.o process.o time.o tty.o user_syms.o drivers/
+obj-y = elf_aux.o file.o process.o time.o tty.o user_syms.o drivers/
-USER_OBJS := $(foreach file,file.o process.o time.o tty.o,$(obj)/$(file))
+USER_OBJS := elf_aux.o file.o process.o time.o tty.o
+USER_OBJS := $(foreach file,$(USER_OBJS),$(obj)/$(file))
$(USER_OBJS) : %.o: %.c
$(CC) $(CFLAGS_$(notdir $@)) $(USER_CFLAGS) -c -o $@ $<
Index: 2.6.9/arch/um/os-Linux/elf_aux.c
===================================================================
--- 2.6.9.orig/arch/um/os-Linux/elf_aux.c 2003-09-15 09:40:47.000000000 -0400
+++ 2.6.9/arch/um/os-Linux/elf_aux.c 2004-12-01 23:44:11.000000000 -0500
@@ -0,0 +1,66 @@
+/*
+ * arch/um/kernel/elf_aux.c
+ *
+ * Scan the Elf auxiliary vector provided by the host to extract
+ * information about vsyscall-page, etc.
+ *
+ * Copyright (C) 2004 Fujitsu Siemens Computers GmbH
+ * Author: Bodo Stroesser (bodo.stroesser@xxxxxxxxxxxxxxxxxxx)
+ */
+#include <elf.h>
+#include <stddef.h>
+#include "init.h"
+
+#if ELF_CLASS == ELFCLASS32
+typedef Elf32_auxv_t elf_auxv_t;
+#else
+typedef Elf64_auxv_t elf_auxv_t;
+#endif
+
+char * elf_aux_platform;
+long elf_aux_hwcap;
+
+long vsyscall_ehdr;
+long vsyscall_end;
+
+long __kernel_vsyscall;
+
+
+__init void scan_elf_aux( char **envp)
+{
+ long page_size = 0;
+ elf_auxv_t * auxv;
+
+ while ( *envp++ != NULL) ;
+
+ for ( auxv = (elf_auxv_t *)envp; auxv->a_type != AT_NULL; auxv++) {
+ switch ( auxv->a_type ) {
+ case AT_SYSINFO:
+ __kernel_vsyscall = auxv->a_un.a_val;
+ break;
+ case AT_SYSINFO_EHDR:
+ vsyscall_ehdr = auxv->a_un.a_val;
+ break;
+ case AT_HWCAP:
+ elf_aux_hwcap = auxv->a_un.a_val;
+ break;
+ case AT_PLATFORM:
+ elf_aux_platform = auxv->a_un.a_ptr;
+ break;
+ case AT_PAGESZ:
+ page_size = auxv->a_un.a_val;
+ break;
+ }
+ }
+ if ( ! __kernel_vsyscall || ! vsyscall_ehdr ||
+ ! elf_aux_hwcap || ! elf_aux_platform ||
+ ! page_size || (vsyscall_ehdr % page_size) ) {
+ __kernel_vsyscall = 0;
+ vsyscall_ehdr = 0;
+ elf_aux_hwcap = 0;
+ elf_aux_platform = "i586";
+ }
+ else {
+ vsyscall_end = vsyscall_ehdr + page_size;
+ }
+}
Index: 2.6.9/include/asm-um/archparam-i386.h
===================================================================
--- 2.6.9.orig/include/asm-um/archparam-i386.h 2004-12-01 23:43:04.000000000 -0500
+++ 2.6.9/include/asm-um/archparam-i386.h 2004-12-01 23:44:11.000000000 -0500
@@ -10,7 +10,8 @@
#include "user.h"
-#define ELF_PLATFORM "i586"
+extern char * elf_aux_platform;
+#define ELF_PLATFORM (elf_aux_platform)
#define ELF_ET_DYN_BASE (2 * TASK_SIZE / 3)
@@ -56,15 +57,13 @@
pr_reg[16] = PT_REGS_SS(regs); \
} while(0);
-#if 0 /* Turn this back on when UML has VSYSCALL working */
-#define VSYSCALL_BASE (__fix_to_virt(FIX_VSYSCALL))
-#else
-#define VSYSCALL_BASE 0
-#endif
-#define VSYSCALL_EHDR ((const struct elfhdr *) VSYSCALL_BASE)
-#define VSYSCALL_ENTRY ((unsigned long) &__kernel_vsyscall)
-extern void *__kernel_vsyscall;
+extern long vsyscall_ehdr;
+extern long vsyscall_end;
+extern long __kernel_vsyscall;
+
+#define VSYSCALL_BASE vsyscall_ehdr
+#define VSYSCALL_END vsyscall_end
/*
* Architecture-neutral AT_ values in 0-17, leave some room
@@ -75,8 +74,10 @@
#define ARCH_DLINFO \
do { \
- NEW_AUX_ENT(AT_SYSINFO, VSYSCALL_ENTRY); \
- NEW_AUX_ENT(AT_SYSINFO_EHDR, VSYSCALL_BASE); \
+ if ( vsyscall_ehdr ) { \
+ NEW_AUX_ENT(AT_SYSINFO, __kernel_vsyscall); \
+ NEW_AUX_ENT(AT_SYSINFO_EHDR, vsyscall_ehdr); \
+ } \
} while (0)
/*
Index: 2.6.9/include/asm-um/elf.h
===================================================================
--- 2.6.9.orig/include/asm-um/elf.h 2004-12-01 23:43:04.000000000 -0500
+++ 2.6.9/include/asm-um/elf.h 2004-12-01 23:44:11.000000000 -0500
@@ -3,7 +3,8 @@
#include "asm/archparam.h"
-#define ELF_HWCAP (0)
+extern long elf_aux_hwcap;
+#define ELF_HWCAP (elf_aux_hwcap)
#define SET_PERSONALITY(ex, ibcs2) do ; while(0)
-
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