um: rework userspace stubs to not hard-code stub location

The userspace stacks mostly have a stack (and in the case of the
syscall stub we can just set their stack pointer) that points to
the location of the stub data page already.

Rework the stubs to use the stack pointer to derive the start of
the data page, rather than requiring it to be hard-coded.

In the clone stub, also integrate the int3 into the stack remap,
since we really must not use the stack while we remap it.

This prepares for putting the stub at a variable location that's
not part of the normal address space of the userspace processes
running inside the UML machine.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

diff --git a/arch/um/include/shared/as-layout.h b/arch/um/include/shared/as-layout.h
index 5f286ef2721b8f214f67c5514b0e6907cc65485a..56408bf3480d685094f1903e98bf6e64baca7025 100644 (file)
--- a/arch/um/include/shared/as-layout.h
+++ b/arch/um/include/shared/as-layout.h
@@ -20,18 +20,10 @@
  * 'UL' and other type specifiers unilaterally.  We
  * use the following macros to deal with this.
  */
-
-#ifdef __ASSEMBLY__
-#define _UML_AC(X, Y)  (Y)
-#else
-#define __UML_AC(X, Y) (X(Y))
-#define _UML_AC(X, Y)  __UML_AC(X, Y)
-#endif
-
-#define STUB_START _UML_AC(, 0x100000)
-#define STUB_CODE _UML_AC((unsigned long), STUB_START)
-#define STUB_DATA _UML_AC((unsigned long), STUB_CODE + UM_KERN_PAGE_SIZE)
-#define STUB_END _UML_AC((unsigned long), STUB_DATA + UM_KERN_PAGE_SIZE)
+#define STUB_START 0x100000UL
+#define STUB_CODE STUB_START
+#define STUB_DATA (STUB_CODE + UM_KERN_PAGE_SIZE)
+#define STUB_END (STUB_DATA + UM_KERN_PAGE_SIZE)
 
 #ifndef __ASSEMBLY__
 

diff --git a/arch/um/include/shared/common-offsets.h b/arch/um/include/shared/common-offsets.h
index 16a51a8c800f478d110a11939439787c40168fa1..edc90ab73734757460e59f05c9dac9067c14f156 100644 (file)
--- a/arch/um/include/shared/common-offsets.h
+++ b/arch/um/include/shared/common-offsets.h
@@ -1,5 +1,6 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 /* for use by sys-$SUBARCH/kernel-offsets.c */
+#include <stub-data.h>
 
 DEFINE(KERNEL_MADV_REMOVE, MADV_REMOVE);
 
@@ -43,3 +44,8 @@ DEFINE(UML_CONFIG_64BIT, CONFIG_64BIT);
 #ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
 DEFINE(UML_CONFIG_UML_TIME_TRAVEL_SUPPORT, CONFIG_UML_TIME_TRAVEL_SUPPORT);
 #endif
+
+/* for stub */
+DEFINE(UML_STUB_FIELD_OFFSET, offsetof(struct stub_data, offset));
+DEFINE(UML_STUB_FIELD_CHILD_ERR, offsetof(struct stub_data, child_err));
+DEFINE(UML_STUB_FIELD_FD, offsetof(struct stub_data, fd));

diff --git a/arch/um/kernel/skas/clone.c b/arch/um/kernel/skas/clone.c
index 7c592c788cbf4a613f3407496f92a4cba540899e..592cdb138441548bd8a474ebb197690187e30175 100644 (file)
--- a/arch/um/kernel/skas/clone.c
+++ b/arch/um/kernel/skas/clone.c
@@ -41,8 +41,7 @@ stub_clone_handler(void)
                goto done;
        }
 
-       remap_stack(data->fd, data->offset);
-       goto done;
+       remap_stack_and_trap();
 
  done:
        trap_myself();

diff --git a/arch/um/os-Linux/skas/mem.c b/arch/um/os-Linux/skas/mem.c
index c546d16f8dfe67bea7ce06f77a9a90e8a3c5e828..3b4975ee67e2d6872f3d7e88a37f1a215f95e47d 100644 (file)
--- a/arch/um/os-Linux/skas/mem.c
+++ b/arch/um/os-Linux/skas/mem.c
@@ -40,6 +40,8 @@ static int __init init_syscall_regs(void)
        syscall_regs[REGS_IP_INDEX] = STUB_CODE +
                ((unsigned long) batch_syscall_stub -
                 (unsigned long) __syscall_stub_start);
+       syscall_regs[REGS_SP_INDEX] = STUB_DATA;
+
        return 0;
 }
 

diff --git a/arch/x86/um/shared/sysdep/stub_32.h b/arch/x86/um/shared/sysdep/stub_32.h
index 8ea69211e53cb80cfc8fb2bcb89acdad3ad5118f..c3891c1ada26c9397d40f4506ba3902c02a30fbb 100644 (file)
--- a/arch/x86/um/shared/sysdep/stub_32.h
+++ b/arch/x86/um/shared/sysdep/stub_32.h
@@ -7,8 +7,8 @@
 #define __SYSDEP_STUB_H
 
 #include <asm/ptrace.h>
+#include <generated/asm-offsets.h>
 
-#define STUB_SYSCALL_RET EAX
 #define STUB_MMAP_NR __NR_mmap2
 #define MMAP_OFFSET(o) ((o) >> UM_KERN_PAGE_SHIFT)
 
@@ -77,17 +77,28 @@ static inline void trap_myself(void)
        __asm("int3");
 }
 
-static inline void remap_stack(int fd, unsigned long offset)
+static void inline remap_stack_and_trap(void)
 {
-       __asm__ volatile ("movl %%eax,%%ebp ; movl %0,%%eax ; int $0x80 ;"
-                         "movl %7, %%ebx ; movl %%eax, (%%ebx)"
-                         : : "g" (STUB_MMAP_NR), "b" (STUB_DATA),
-                           "c" (UM_KERN_PAGE_SIZE),
-                           "d" (PROT_READ | PROT_WRITE),
-                           "S" (MAP_FIXED | MAP_SHARED), "D" (fd),
-                           "a" (offset),
-                           "i" (&((struct stub_data *) STUB_DATA)->child_err)
-                         : "memory");
+       __asm__ volatile (
+               "movl %%esp,%%ebx ;"
+               "andl %0,%%ebx ;"
+               "movl %1,%%eax ;"
+               "movl %%ebx,%%edi ; addl %2,%%edi ; movl (%%edi),%%edi ;"
+               "movl %%ebx,%%ebp ; addl %3,%%ebp ; movl (%%ebp),%%ebp ;"
+               "int $0x80 ;"
+               "addl %4,%%ebx ; movl %%eax, (%%ebx) ;"
+               "int $3"
+               : :
+               "g" (~(UM_KERN_PAGE_SIZE - 1)),
+               "g" (STUB_MMAP_NR),
+               "g" (UML_STUB_FIELD_FD),
+               "g" (UML_STUB_FIELD_OFFSET),
+               "g" (UML_STUB_FIELD_CHILD_ERR),
+               "c" (UM_KERN_PAGE_SIZE),
+               "d" (PROT_READ | PROT_WRITE),
+               "S" (MAP_FIXED | MAP_SHARED)
+               :
+               "memory");
 }
 
 #endif

diff --git a/arch/x86/um/shared/sysdep/stub_64.h b/arch/x86/um/shared/sysdep/stub_64.h
index b7b8b8e4359dfb0749953eca9dae93796a1685f2..6e2626b77a2e42c3f77549333655723794417965 100644 (file)
--- a/arch/x86/um/shared/sysdep/stub_64.h
+++ b/arch/x86/um/shared/sysdep/stub_64.h
@@ -7,8 +7,8 @@
 #define __SYSDEP_STUB_H
 
 #include <sysdep/ptrace_user.h>
+#include <generated/asm-offsets.h>
 
-#define STUB_SYSCALL_RET PT_INDEX(RAX)
 #define STUB_MMAP_NR __NR_mmap
 #define MMAP_OFFSET(o) (o)
 
@@ -82,18 +82,30 @@ static inline void trap_myself(void)
        __asm("int3");
 }
 
-static inline void remap_stack(long fd, unsigned long offset)
+static inline void remap_stack_and_trap(void)
 {
-       __asm__ volatile ("movq %4,%%r10 ; movq %5,%%r8 ; "
-                         "movq %6, %%r9; " __syscall "; movq %7, %%rbx ; "
-                         "movq %%rax, (%%rbx)":
-                         : "a" (STUB_MMAP_NR), "D" (STUB_DATA),
-                           "S" (UM_KERN_PAGE_SIZE),
-                           "d" (PROT_READ | PROT_WRITE),
-                            "g" (MAP_FIXED | MAP_SHARED), "g" (fd),
-                           "g" (offset),
-                           "i" (&((struct stub_data *) STUB_DATA)->child_err)
-                         : __syscall_clobber, "r10", "r8", "r9" );
+       __asm__ volatile (
+               "movq %0,%%rax ;"
+               "movq %%rsp,%%rdi ;"
+               "andq %1,%%rdi ;"
+               "movq %2,%%r10 ;"
+               "movq %%rdi,%%r8 ; addq %3,%%r8 ; movq (%%r8),%%r8 ;"
+               "movq %%rdi,%%r9 ; addq %4,%%r9 ; movq (%%r9),%%r9 ;"
+               __syscall ";"
+               "movq %%rsp,%%rdi ; andq %1,%%rdi ;"
+               "addq %5,%%rdi ; movq %%rax, (%%rdi) ;"
+               "int3"
+               : :
+               "g" (STUB_MMAP_NR),
+               "g" (~(UM_KERN_PAGE_SIZE - 1)),
+               "g" (MAP_FIXED | MAP_SHARED),
+               "g" (UML_STUB_FIELD_FD),
+               "g" (UML_STUB_FIELD_OFFSET),
+               "g" (UML_STUB_FIELD_CHILD_ERR),
+               "S" (UM_KERN_PAGE_SIZE),
+               "d" (PROT_READ | PROT_WRITE)
+               :
+               __syscall_clobber, "r10", "r8", "r9");
 }
 
 #endif

diff --git a/arch/x86/um/stub_32.S b/arch/x86/um/stub_32.S
index a193e88536a904a54abf4177323e2d871825423a..8291899e6aafde0a013f8db2647e227d24c08df8 100644 (file)
--- a/arch/x86/um/stub_32.S
+++ b/arch/x86/um/stub_32.S
@@ -5,21 +5,22 @@
 
        .globl batch_syscall_stub
 batch_syscall_stub:
-       /* load pointer to first operation */
-       mov     $(STUB_DATA+8), %esp
-
+       /* %esp comes in as "top of page" */
+       mov %esp, %ecx
+       /* %esp has pointer to first operation */
+       add $8, %esp
 again:
        /* load length of additional data */
        mov     0x0(%esp), %eax
 
        /* if(length == 0) : end of list */
        /* write possible 0 to header */
-       mov     %eax, STUB_DATA+4
+       mov     %eax, 0x4(%ecx)
        cmpl    $0, %eax
        jz      done
 
        /* save current pointer */
-       mov     %esp, STUB_DATA+4
+       mov     %esp, 0x4(%ecx)
 
        /* skip additional data */
        add     %eax, %esp
@@ -38,6 +39,10 @@ again:
        /* execute syscall */
        int     $0x80
 
+       /* restore top of page pointer in %ecx */
+       mov     %esp, %ecx
+       andl    $(~UM_KERN_PAGE_SIZE) + 1, %ecx
+
        /* check return value */
        pop     %ebx
        cmp     %ebx, %eax
@@ -45,7 +50,7 @@ again:
 
 done:
        /* save return value */
-       mov     %eax, STUB_DATA
+       mov     %eax, (%ecx)
 
        /* stop */
        int3

diff --git a/arch/x86/um/stub_64.S b/arch/x86/um/stub_64.S
index 8a95c5b2eaf93266a64543ae2fa86cfdecff89b0..f3404640197a50a14d4e16c8b2b67f119298f07b 100644 (file)
--- a/arch/x86/um/stub_64.S
+++ b/arch/x86/um/stub_64.S
@@ -4,9 +4,8 @@
 .section .__syscall_stub, "ax"
        .globl batch_syscall_stub
 batch_syscall_stub:
-       mov     $(STUB_DATA), %rbx
-       /* load pointer to first operation */
-       mov     %rbx, %rsp
+       /* %rsp has the pointer to first operation */
+       mov     %rsp, %rbx
        add     $0x10, %rsp
 again:
        /* load length of additional data */

diff --git a/arch/x86/um/stub_segv.c b/arch/x86/um/stub_segv.c
index 27361cbb7ca9bed47194fe4127e231a8d3c39c0d..21836eaf1725914ef24d0488bb5beb10b8491357 100644 (file)
--- a/arch/x86/um/stub_segv.c
+++ b/arch/x86/um/stub_segv.c
@@ -11,10 +11,11 @@
 void __attribute__ ((__section__ (".__syscall_stub")))
 stub_segv_handler(int sig, siginfo_t *info, void *p)
 {
+       int stack;
        ucontext_t *uc = p;
+       struct faultinfo *f = (void *)(((unsigned long)&stack) & ~(UM_KERN_PAGE_SIZE - 1));
 
-       GET_FAULTINFO_FROM_MC(*((struct faultinfo *) STUB_DATA),
-                             &uc->uc_mcontext);
+       GET_FAULTINFO_FROM_MC(*f, &uc->uc_mcontext);
        trap_myself();
 }