[PATCH v3 6/9] livepatch: Add parsing for the symbol+0x<offset>/<len>

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

in case we want to patch at specific offsets inside
a function. (for example if we want to do NOP patching).

We also assume that the 'len' is only the size of
an isns that would be for a call opcode (so 5 bytes
on x86, and 4 on ARM 32/64).

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
---
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Ross Lagerwall <ross.lagerwall@citrix.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Julien Grall <julien.grall@arm.com>
Cc: Jan Beulich <jbeulich@suse.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>

v3: First submission
---
 docs/misc/livepatch.markdown |  2 +-
 xen/arch/arm/livepatch.c     |  8 ++++++++
 xen/arch/x86/livepatch.c     |  5 +++++
 xen/common/livepatch.c       | 43 +++++++++++++++++++++++++++++++++++++++++--
 xen/include/xen/livepatch.h  |  1 +
 5 files changed, 56 insertions(+), 3 deletions(-)

diff --git a/docs/misc/livepatch.markdown b/docs/misc/livepatch.markdown
index 89c1050..f1a5147 100644
--- a/docs/misc/livepatch.markdown
+++ b/docs/misc/livepatch.markdown
@@ -312,7 +312,7 @@ The size of the structure is 64 bytes on 64-bit hypervisors. It will be
 
 * `name` is the symbol name of the old function. Only used if `old_addr` is
    zero, otherwise will be used during dynamic linking (when hypervisor loads
-   the payload).
+   the payload). The format can be _symbol_ or _symbol+0x<offset>/<len>_.
 
 * `old_addr` is the address of the function to be patched and is filled in at
   payload generation time if hypervisor function address is known. If unknown,
diff --git a/xen/arch/arm/livepatch.c b/xen/arch/arm/livepatch.c
index aba1320..3093554 100644
--- a/xen/arch/arm/livepatch.c
+++ b/xen/arch/arm/livepatch.c
@@ -7,6 +7,14 @@
 #include <xen/livepatch_elf.h>
 #include <xen/livepatch.h>
 
+/* On ARM32,64 instructions are always 4 bytes long. */
+#define PATCH_INSN_SIZE 4
+
+int arch_verify_insn_length(unsigned long len)
+{
+    return len != PATCH_INSN_SIZE;
+}
+
 void arch_livepatch_quiesce(void)
 {
 }
diff --git a/xen/arch/x86/livepatch.c b/xen/arch/x86/livepatch.c
index 1023fab..df64b00 100644
--- a/xen/arch/x86/livepatch.c
+++ b/xen/arch/x86/livepatch.c
@@ -27,6 +27,11 @@ void arch_livepatch_revive(void)
     write_cr0(read_cr0() | X86_CR0_WP);
 }
 
+int arch_verify_insn_length(unsigned long len)
+{
+    return len != PATCH_INSN_SIZE;
+}
+
 int arch_livepatch_verify_func(const struct livepatch_func *func)
 {
     /* No NOP patching yet. */
diff --git a/xen/common/livepatch.c b/xen/common/livepatch.c
index cbfeac1..e752949 100644
--- a/xen/common/livepatch.c
+++ b/xen/common/livepatch.c
@@ -234,14 +234,46 @@ static const char *livepatch_symbols_lookup(unsigned long addr,
 
 static int lookup_symbol(struct livepatch_func *f, struct livepatch_elf *elf)
 {
+    const char *s;
+    char *plus = NULL, *slash = NULL;
+    unsigned long offset = 0;
+
     if ( f->old_addr )
         return 0;
 
+    s = f->name;
+    /* +<offset>/<len> */
+    plus = strchr(f->name, '+');
+    if ( plus )
+    {
+        slash = strchr(plus, '/');
+
+        if ( slash )
+        {
+            const char *endp = NULL;
+            unsigned int len;
+
+            offset = simple_strtoul(plus+1, &endp, 16);
+
+            if ( endp != slash )
+                return -EINVAL;
+
+            len = simple_strtoul(slash+1, NULL, 16);
+
+            if ( arch_verify_insn_length(len) )
+                return -EINVAL;
+
+            /* So that symbol lookup works. */
+            *plus = '\0';
+            s = f->name;
+        }
+    }
+
     /* Lookup function's old address if not already resolved. */
-    f->old_addr = (void *)symbols_lookup_by_name(f->name);
+    f->old_addr = (void *)symbols_lookup_by_name(s);
     if ( !f->old_addr )
     {
-        f->old_addr = (void *)livepatch_symbols_lookup_by_name(f->name);
+        f->old_addr = (void *)livepatch_symbols_lookup_by_name(s);
         if ( !f->old_addr )
         {
             dprintk(XENLOG_ERR, LIVEPATCH "%s: Could not resolve old address of %s\n",
@@ -249,6 +281,13 @@ static int lookup_symbol(struct livepatch_func *f, struct livepatch_elf *elf)
             return -ENOENT;
         }
     }
+
+    if ( plus && slash )
+    {
+        *plus = '+';
+        f->old_addr += offset;
+    }
+
     dprintk(XENLOG_DEBUG, LIVEPATCH "%s: Resolved old address %s => %p\n",
             elf->name, f->name, f->old_addr);
 
diff --git a/xen/include/xen/livepatch.h b/xen/include/xen/livepatch.h
index 02f4572..2e64686 100644
--- a/xen/include/xen/livepatch.h
+++ b/xen/include/xen/livepatch.h
@@ -44,6 +44,7 @@ unsigned long livepatch_symbols_lookup_by_name(const char *symname);
 bool_t is_patch(const void *addr);
 
 /* Arch hooks. */
+int arch_verify_insn_length(unsigned long len);
 int arch_livepatch_verify_elf(const struct livepatch_elf *elf);
 int arch_livepatch_perform_rel(struct livepatch_elf *elf,
                                const struct livepatch_elf_sec *base,
-- 
2.4.11


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