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Date: Thu, 12 Nov 2015 13:45:49 -0600
From: Josh Poimboeuf <jpoimboe@...hat.com>
To: Chris J Arges <chris.j.arges@...onical.com>
Cc: live-patching@...r.kernel.org, jeyu@...hat.com,
Seth Jennings <sjenning@...hat.com>,
Jiri Kosina <jikos@...nel.org>,
Vojtech Pavlik <vojtech@...e.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4 v5] livepatch: add old_sympos as disambiguator field
to klp_func
On Thu, Nov 12, 2015 at 10:59:50AM -0600, Chris J Arges wrote:
> In cases of duplicate symbols, old_sympos will be used to disambiguate
> instead of old_addr. By default old_sympos will be 0, and patching will
> only succeed if the symbol is unique. Specifying a positive value will
> ensure that occurrence of the symbol in kallsyms for the patched object
> will be used for patching if it is valid.
>
> In addition, make old_addr an internal structure field not to be specified
> by the user. Finally, remove klp_find_verify_func_addr as it can be
> replaced by klp_find_object_symbol directly.
>
> Signed-off-by: Chris J Arges <chris.j.arges@...onical.com>
> ---
> include/linux/livepatch.h | 20 ++++++++-------
> kernel/livepatch/core.c | 65 ++++++++++++++++++++---------------------------
> 2 files changed, 38 insertions(+), 47 deletions(-)
>
> diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
> index 31db7a0..3d18dff 100644
> --- a/include/linux/livepatch.h
> +++ b/include/linux/livepatch.h
> @@ -37,8 +37,9 @@ enum klp_state {
> * struct klp_func - function structure for live patching
> * @old_name: name of the function to be patched
> * @new_func: pointer to the patched function code
> - * @old_addr: a hint conveying at what address the old function
> - * can be found (optional, vmlinux patches only)
> + * @old_sympos: a hint indicating which symbol position the old function
> + * can be found (optional)
> + * @old_addr: the address of the function being patched
> * @kobj: kobject for sysfs resources
> * @state: tracks function-level patch application state
> * @stack_node: list node for klp_ops func_stack list
> @@ -47,17 +48,18 @@ struct klp_func {
> /* external */
> const char *old_name;
> void *new_func;
> +
> /*
> - * The old_addr field is optional and can be used to resolve
> - * duplicate symbol names in the vmlinux object. If this
> - * information is not present, the symbol is located by name
> - * with kallsyms. If the name is not unique and old_addr is
> - * not provided, the patch application fails as there is no
> - * way to resolve the ambiguity.
> + * The old_sympos field is optional and can be used to resolve
> + * duplicate symbol names in livepatch objects. If this field is zero,
> + * it is expected the symbol is unique, otherwise patching fails. If
> + * this value is greater than zero then that occurrence of the symbol
> + * in kallsyms for the given object is used.
> */
> - unsigned long old_addr;
> + unsigned long old_sympos;
>
> /* internal */
> + unsigned long old_addr;
> struct kobject kobj;
> enum klp_state state;
> struct list_head stack_node;
> diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> index 6e53441..479d75e 100644
> --- a/kernel/livepatch/core.c
> +++ b/kernel/livepatch/core.c
> @@ -135,13 +135,8 @@ struct klp_find_arg {
> const char *objname;
> const char *name;
> unsigned long addr;
> - /*
> - * If count == 0, the symbol was not found. If count == 1, a unique
> - * match was found and addr is set. If count > 1, there is
> - * unresolvable ambiguity among "count" number of symbols with the same
> - * name in the same object.
> - */
> unsigned long count;
> + unsigned long pos;
> };
>
> static int klp_find_callback(void *data, const char *name,
> @@ -159,36 +154,46 @@ static int klp_find_callback(void *data, const char *name,
> return 0;
>
> /*
> - * args->addr might be overwritten if another match is found
> - * but klp_find_object_symbol() handles this and only returns the
> - * addr if count == 1.
> + * Increment and assign the address. Return 1 when the desired symbol
> + * position is found or the search for a unique symbol fails.
> */
> args->addr = addr;
> args->count++;
> + if (((args->pos > 0) && (args->count == args->pos)) ||
> + ((args->pos == 0) && (args->count > 1)))
> + return 1;
>
> return 0;
> }
>
> static int klp_find_object_symbol(const char *objname, const char *name,
> - unsigned long *addr)
> + unsigned long *addr, unsigned long sympos)
One nit about this interface. I think it would be clearer if the sympos
argument came before the addr argument:
static int klp_find_object_symbol(const char *objname, const char *name,
unsigned long sympos, unsigned long addr)
Because:
1. it puts all input arguments before the output argument; and
2. it puts the sympos in its logical place immediately after the
function name.
--
Josh
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