[Xen-devel] [PATCH v4 6/9] livepatch: Add parsing for the symbol+0x<offset>

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

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

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
---
Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Cc: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Cc: Julien Grall <julien.grall@xxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

v3: First submission
v4: Drop the /<len> part of the symbol.
---
 docs/misc/livepatch.markdown |  2 +-
 xen/common/livepatch.c       | 32 ++++++++++++++++++++++++++++++--
 xen/include/xen/livepatch.h  |  1 +
 3 files changed, 32 insertions(+), 3 deletions(-)

diff --git a/docs/misc/livepatch.markdown b/docs/misc/livepatch.markdown
index 89c1050..7e82047 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>_.
 
 * `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/common/livepatch.c b/xen/common/livepatch.c
index e5968a7..c234424 100644
--- a/xen/common/livepatch.c
+++ b/xen/common/livepatch.c
@@ -237,13 +237,34 @@ static const char *livepatch_symbols_lookup(unsigned long 
addr,
 static int resolve_old_address(struct livepatch_func *f,
                                const struct livepatch_elf *elf)
 {
+    const char *s;
+    char *plus = NULL;
+    unsigned long offset = 0;
+
     if ( f->old_addr )
         return 0;
 
-    f->old_addr = (void *)symbols_lookup_by_name(f->name);
+    s = f->name;
+    /* +<offset> */
+    plus = strchr(f->name, '+');
+    if ( plus )
+    {
+        const char *endp = NULL;
+
+        offset = simple_strtoul(plus + 1, &endp, 16);
+
+        if ( *endp != '\0' )
+            return -EINVAL;
+
+        /* So that symbol lookup works. */
+        *plus = '\0';
+        s = 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",
@@ -251,6 +272,13 @@ static int resolve_old_address(struct livepatch_func *f,
             return -ENOENT;
         }
     }
+
+    if ( plus )
+    {
+        *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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