[S390] Mark kernel text section read-only.

Set read-only flag in the page table entries for the kernel image text
section. This will catch all instruction caused corruptions withing the
text section.
Instruction replacement via kprobes still works, since it bypasses now
dynamic address translation.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

diff --git a/arch/s390/kernel/early.c b/arch/s390/kernel/early.c
index 40dd47970a332fd52e64d64933a5dcc4b998db13..e518dd53eff52408f0b7427d181efd4715145e75 100644 (file)
--- a/arch/s390/kernel/early.c
+++ b/arch/s390/kernel/early.c
@@ -27,7 +27,6 @@
 #define DEFSYS_CMD_SIZE                96
 #define SAVESYS_CMD_SIZE       32
 
-extern int _eshared;
 char kernel_nss_name[NSS_NAME_SIZE + 1];
 
 #ifdef CONFIG_SHARED_KERNEL

diff --git a/arch/s390/kernel/kprobes.c b/arch/s390/kernel/kprobes.c
index b2e1dc89a8c6e4be3d84affbac6dd2d9e00fb728..a466bab6677e15f506da1fb3d8168d5792170167 100644 (file)
--- a/arch/s390/kernel/kprobes.c
+++ b/arch/s390/kernel/kprobes.c
@@ -155,15 +155,34 @@ void __kprobes get_instruction_type(struct arch_specific_insn *ainsn)
 static int __kprobes swap_instruction(void *aref)
 {
        struct ins_replace_args *args = aref;
+       u32 *addr;
+       u32 instr;
        int err = -EFAULT;
 
+       /*
+        * Text segment is read-only, hence we use stura to bypass dynamic
+        * address translation to exchange the instruction. Since stura
+        * always operates on four bytes, but we only want to exchange two
+        * bytes do some calculations to get things right. In addition we
+        * shall not cross any page boundaries (vmalloc area!) when writing
+        * the new instruction.
+        */
+       addr = (u32 *)ALIGN((unsigned long)args->ptr, 4);
+       if ((unsigned long)args->ptr & 2)
+               instr = ((*addr) & 0xffff0000) | args->new;
+       else
+               instr = ((*addr) & 0x0000ffff) | args->new << 16;
+
        asm volatile(
-               "0: mvc  0(2,%2),0(%3)\n"
-               "1: la   %0,0\n"
+               "       lra     %1,0(%1)\n"
+               "0:     stura   %2,%1\n"
+               "1:     la      %0,0\n"
                "2:\n"
                EX_TABLE(0b,2b)
-               : "+d" (err), "=m" (*args->ptr)
-               : "a" (args->ptr), "a" (&args->new), "m" (args->new));
+               : "+d" (err)
+               : "a" (addr), "d" (instr)
+               : "memory", "cc");
+
        return err;
 }
 

diff --git a/arch/s390/kernel/vmlinux.lds.S b/arch/s390/kernel/vmlinux.lds.S
index 8fedb1f9fc976572c27f3863821e0ad60256021e..a4890739252230df4ebb28cc70a0e79915aa7bd0 100644 (file)
--- a/arch/s390/kernel/vmlinux.lds.S
+++ b/arch/s390/kernel/vmlinux.lds.S
@@ -35,9 +35,10 @@ SECTIONS
 
 #ifdef CONFIG_SHARED_KERNEL
   . = ALIGN(1048576);          /* VM shared segments are 1MB aligned */
+#endif
 
+  . = ALIGN(4096);
   _eshared = .;                        /* End of shareable data */
-#endif
 
   . = ALIGN(16);               /* Exception table */
   __start___ex_table = .;

diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
index 162a338a5575a6f8b549669da50e82a5861326c7..b3e7c45efb63110f064ab77693e5349b71d081de 100644 (file)
--- a/arch/s390/mm/init.c
+++ b/arch/s390/mm/init.c
@@ -26,7 +26,6 @@
 #include <linux/pfn.h>
 #include <linux/poison.h>
 #include <linux/initrd.h>
-
 #include <asm/processor.h>
 #include <asm/system.h>
 #include <asm/uaccess.h>
@@ -96,8 +95,8 @@ static void __init setup_ro_region(void)
        pte_t new_pte;
        unsigned long address, end;
 
-       address = ((unsigned long)&__start_rodata) & PAGE_MASK;
-       end = PFN_ALIGN((unsigned long)&__end_rodata);
+       address = ((unsigned long)&_stext) & PAGE_MASK;
+       end = PFN_ALIGN((unsigned long)&_eshared);
 
        for (; address < end; address += PAGE_SIZE) {
                pgd = pgd_offset_k(address);
@@ -173,8 +172,8 @@ void __init mem_init(void)
                 datasize >>10,
                 initsize >> 10);
        printk("Write protected kernel read-only data: %#lx - %#lx\n",
-              (unsigned long)&__start_rodata,
-              PFN_ALIGN((unsigned long)&__end_rodata) - 1);
+              (unsigned long)&_stext,
+              PFN_ALIGN((unsigned long)&_eshared) - 1);
 }
 
 void free_initmem(void)

diff --git a/include/asm-s390/sections.h b/include/asm-s390/sections.h
index 3a0b8ffeab7af2cf1c6e6cafb2e709e97319ae2e..1c5a2c4ccdad29af3ccb5c0ed4436b79522cf128 100644 (file)
--- a/include/asm-s390/sections.h
+++ b/include/asm-s390/sections.h
@@ -3,4 +3,6 @@
 
 #include <asm-generic/sections.h>
 
+extern char _eshared[];
+
 #endif