[PATCH v7 16/24] xsplice: Add support for alternatives

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

From: Ross Lagerwall <ross.lagerwall@citrix.com>

Add support for applying alternative sections within xsplice payload.
At payload load time, apply an alternative sections that are found.

Also we add an test-case exercising a rather useless alternative
(patching a NOP with a NOP) - but it does exercise the code-path.

Signed-off-by: Ross Lagerwall <ross.lagerwall@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

---
Cc: Keir Fraser <keir@xen.org>
Cc: Jan Beulich <jbeulich@suse.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>

v2: Make a new alternative function that does not ASSERT on IRQs and
    don't disable IRQs in the code when loading payload.
v4: Include test-case
    Include check for size of alternatives and that it is not a 0 size
    section.
v6: Add #define INIT to preserve __initness on alternative code.
    Double check that alt_instr are only patching payload code.
v7: Move cr0 manipulation in apply_alternatives.
    ifdef around alternative.o in Makefile
    Pick X86_FEATURE_LM in test-case
    Drop casting from load_addr
    It is alternative.init.o, not alternative_init.o (thanks Andrew!)
---
---
 xen/arch/x86/Makefile                    |  4 +++
 xen/arch/x86/alternative.c               | 42 ++++++++++++++++++++------------
 xen/arch/x86/test/xen_hello_world_func.c |  5 ++++
 xen/common/xsplice.c                     | 34 ++++++++++++++++++++++++++
 xen/include/asm-x86/alternative.h        |  4 +++
 5 files changed, 74 insertions(+), 15 deletions(-)

diff --git a/xen/arch/x86/Makefile b/xen/arch/x86/Makefile
index 57c93e1..d210bb7 100644
--- a/xen/arch/x86/Makefile
+++ b/xen/arch/x86/Makefile
@@ -6,7 +6,11 @@ subdir-y += mm
 subdir-$(CONFIG_XENOPROF) += oprofile
 subdir-y += x86_64
 
+ifdef CONFIG_XSPLICE
+obj-y += alternative.o
+else
 obj-bin-y += alternative.init.o
+endif
 obj-y += apic.o
 obj-y += bitops.o
 obj-bin-y += bzimage.init.o
diff --git a/xen/arch/x86/alternative.c b/xen/arch/x86/alternative.c
index f735ff8..366ad86 100644
--- a/xen/arch/x86/alternative.c
+++ b/xen/arch/x86/alternative.c
@@ -22,13 +22,14 @@
 #include <asm/system.h>
 #include <asm/traps.h>
 #include <asm/nmi.h>
+#include <xen/xsplice.h>
 
 #define MAX_PATCH_LEN (255-1)
 
 extern struct alt_instr __alt_instructions[], __alt_instructions_end[];
 
 #ifdef K8_NOP1
-static const unsigned char k8nops[] __initconst = {
+static const unsigned char k8nops[] __INITCONST = {
     K8_NOP1,
     K8_NOP2,
     K8_NOP3,
@@ -52,7 +53,7 @@ static const unsigned char * const k8_nops[ASM_NOP_MAX+1] __initconstrel = {
 #endif
 
 #ifdef P6_NOP1
-static const unsigned char p6nops[] __initconst = {
+static const unsigned char p6nops[] __INITCONST = {
     P6_NOP1,
     P6_NOP2,
     P6_NOP3,
@@ -75,7 +76,7 @@ static const unsigned char * const p6_nops[ASM_NOP_MAX+1] __initconstrel = {
 };
 #endif
 
-static const unsigned char * const *ideal_nops __initdata = k8_nops;
+static const unsigned char * const *ideal_nops __INITDATA = k8_nops;
 
 static int __init mask_nmi_callback(const struct cpu_user_regs *regs, int cpu)
 {
@@ -100,7 +101,7 @@ static void __init arch_init_ideal_nops(void)
 }
 
 /* Use this to add nops to a buffer, then text_poke the whole buffer. */
-static void __init add_nops(void *insns, unsigned int len)
+static void __INIT add_nops(void *insns, unsigned int len)
 {
     while ( len > 0 )
     {
@@ -114,7 +115,7 @@ static void __init add_nops(void *insns, unsigned int len)
 }
 
 /*
- * text_poke_early - Update instructions on a live kernel at boot time
+ * text_poke - Update instructions on a live kernel or non-executed code.
  * @addr: address to modify
  * @opcode: source of the copy
  * @len: length to copy
@@ -125,9 +126,10 @@ static void __init add_nops(void *insns, unsigned int len)
  * instructions. And on the local CPU you need to be protected again NMI or MCE
  * handlers seeing an inconsistent instruction while you patch.
  *
- * This routine is called with local interrupt disabled.
+ * You should run this with interrupts disabled or on code that has never
+ * been executed.
  */
-static void *__init text_poke_early(void *addr, const void *opcode, size_t len)
+static void *__INIT text_poke(void *addr, const void *opcode, size_t len)
 {
     memcpy(addr, opcode, len);
     sync_core();
@@ -142,20 +144,14 @@ static void *__init text_poke_early(void *addr, const void *opcode, size_t len)
  * APs have less capabilities than the boot processor are not handled.
  * Tough. Make sure you disable such features by hand.
  */
-static void __init apply_alternatives(struct alt_instr *start, struct alt_instr *end)
+void __INIT apply_alternatives_nocheck(struct alt_instr *start, struct alt_instr *end)
 {
     struct alt_instr *a;
     u8 *instr, *replacement;
     u8 insnbuf[MAX_PATCH_LEN];
-    unsigned long cr0 = read_cr0();
-
-    ASSERT(!local_irq_is_enabled());
 
     printk(KERN_INFO "alt table %p -> %p\n", start, end);
 
-    /* Disable WP to allow application of alternatives to read-only pages. */
-    write_cr0(cr0 & ~X86_CR0_WP);
-
     /*
      * The scan order should be from start to end. A later scanned
      * alternative code can overwrite a previous scanned alternative code.
@@ -183,8 +179,24 @@ static void __init apply_alternatives(struct alt_instr *start, struct alt_instr
 
         add_nops(insnbuf + a->replacementlen,
                  a->instrlen - a->replacementlen);
-        text_poke_early(instr, insnbuf, a->instrlen);
+        text_poke(instr, insnbuf, a->instrlen);
     }
+}
+
+/*
+ * This routine is called with local interrupt disabled and used during
+ * bootup.
+ */
+void __init apply_alternatives(struct alt_instr *start, struct alt_instr *end)
+{
+    unsigned long cr0 = read_cr0();
+
+    ASSERT(!local_irq_is_enabled());
+
+    /* Disable WP to allow application of alternatives to read-only pages. */
+    write_cr0(cr0 & ~X86_CR0_WP);
+
+    apply_alternatives_nocheck(start, end);
 
     /* Reinstate WP. */
     write_cr0(cr0);
diff --git a/xen/arch/x86/test/xen_hello_world_func.c b/xen/arch/x86/test/xen_hello_world_func.c
index 432954f..b57822a 100644
--- a/xen/arch/x86/test/xen_hello_world_func.c
+++ b/xen/arch/x86/test/xen_hello_world_func.c
@@ -3,6 +3,9 @@
  *
  */
 
+#include <asm/alternative.h>
+#include <asm/nops.h>
+#include <asm/uaccess.h>
 #include <xen/types.h>
 
 static unsigned long *non_canonical_addr = (unsigned long *)(0xdead000000000000ULL);
@@ -12,6 +15,8 @@ const char *xen_hello_world(void)
 {
     unsigned long tmp;
     int rc;
+
+    alternative(ASM_NOP1, ASM_NOP1, X86_FEATURE_LM);
     /*
      * Any BUG, or WARN_ON will contain symbol and payload name. Furthermore
      * exceptions will be caught and processed properly.
diff --git a/xen/common/xsplice.c b/xen/common/xsplice.c
index c7f70c3..cbbb23d 100644
--- a/xen/common/xsplice.c
+++ b/xen/common/xsplice.c
@@ -530,6 +530,39 @@ static int prepare_payload(struct payload *payload,
     }
 
 #ifndef CONFIG_ARM
+    sec = xsplice_elf_sec_by_name(elf, ".altinstructions");
+    if ( sec )
+    {
+        struct alt_instr *a, *start, *end;
+
+        if ( !sec->sec->sh_size ||
+             (sec->sec->sh_size % sizeof(*a)) )
+        {
+            dprintk(XENLOG_DEBUG, XSPLICE "%s: Wrong size of .alt_instr (exp:%lu vs %lu)!\n",
+                    elf->name, sizeof(*a),
+                    sec->sec->sh_size);
+            return -EINVAL;
+        }
+
+        start = sec->load_addr;
+        end = sec->load_addr + sec->sec->sh_size;
+
+        for ( a = start; a < end; a++ )
+        {
+            unsigned long instr = (unsigned long)(&a->instr_offset + a->instr_offset);
+            unsigned long replacement = (unsigned long)(&a->repl_offset + a->repl_offset);
+
+            if ( (instr < region->start && instr >= region->end) ||
+                 (replacement < region->start && replacement >= region->end) )
+            {
+                dprintk(XENLOG_DEBUG, XSPLICE "%s Alt patching outside payload: 0x%lx!\n",
+                        elf->name, instr);
+                return -EINVAL;
+            }
+        }
+        apply_alternatives_nocheck(start, end);
+    }
+
     sec = xsplice_elf_sec_by_name(elf, ".ex_table");
     if ( sec )
     {
@@ -552,6 +585,7 @@ static int prepare_payload(struct payload *payload,
         region->ex = s;
         region->ex_end = e;
     }
+
 #endif
 
     return 0;
diff --git a/xen/include/asm-x86/alternative.h b/xen/include/asm-x86/alternative.h
index 1056630..bce959f 100644
--- a/xen/include/asm-x86/alternative.h
+++ b/xen/include/asm-x86/alternative.h
@@ -23,6 +23,10 @@ struct alt_instr {
     u8  replacementlen;     /* length of new instruction, <= instrlen */
 };
 
+/* Similar to apply_alternatives except it can be run with IRQs enabled. */
+extern void apply_alternatives_nocheck(struct alt_instr *start,
+                                       struct alt_instr *end);
+extern void apply_alternatives(struct alt_instr *start, struct alt_instr *end);
 extern void alternative_instructions(void);
 
 #define OLDINSTR(oldinstr)      "661:\n\t" oldinstr "\n662:\n"
-- 
2.5.0


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