Re: [PATCH v2 3/5] xen/livepatch: fix norevert test attempt to open-code revert

[Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>]

On Tue, Feb 27, 2024 at 11:25 AM Roger Pau Monne <roger.pau@xxxxxxxxxx> wrote:
>
> The purpose of the norevert test is to install a dummy handler that replaces
> the internal Xen revert code, and then perform the revert in the post-revert
> hook.  For that purpose the usage of the previous common_livepatch_revert() is
> not enough, as that just reverts specific functions, but not the whole state 
> of
> the payload.
>
> Remove both common_livepatch_{apply,revert}() and instead expose
> revert_payload{,_tail}() in order to perform the patch revert from the
> post-revert hook.
>
> Fixes: 6047104c3ccc ('livepatch: Add per-function applied/reverted state 
> tracking marker')
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> ---
> Changes since v1:
>  - Check return value of revert_payload().
> ---
>  xen/common/livepatch.c                        | 41 +++++++++++++++++--
>  xen/include/xen/livepatch.h                   | 32 ++-------------
>  .../livepatch/xen_action_hooks_norevert.c     | 22 +++-------
>  3 files changed, 46 insertions(+), 49 deletions(-)
>
> diff --git a/xen/common/livepatch.c b/xen/common/livepatch.c
> index 14295bae8704..5a7d5b7be0ad 100644
> --- a/xen/common/livepatch.c
> +++ b/xen/common/livepatch.c
> @@ -1366,7 +1366,22 @@ static int apply_payload(struct payload *data)
>      ASSERT(!local_irq_is_enabled());
>
>      for ( i = 0; i < data->nfuncs; i++ )
> -        common_livepatch_apply(&data->funcs[i], &data->fstate[i]);
> +    {
> +        const struct livepatch_func *func = &data->funcs[i];
> +        struct livepatch_fstate *state = &data->fstate[i];
> +
> +        /* If the action has been already executed on this function, do 
> nothing. */
> +        if ( state->applied == LIVEPATCH_FUNC_APPLIED )
> +        {
> +            printk(XENLOG_WARNING LIVEPATCH
> +                   "%s: %s has been already applied before\n",
> +                   __func__, func->name);
> +            continue;
> +        }
> +
> +        arch_livepatch_apply(func, state);
> +        state->applied = LIVEPATCH_FUNC_APPLIED;
> +    }
>
>      arch_livepatch_revive();
>
> @@ -1382,7 +1397,7 @@ static inline void apply_payload_tail(struct payload 
> *data)
>      data->state = LIVEPATCH_STATE_APPLIED;
>  }
>
> -static int revert_payload(struct payload *data)
> +int revert_payload(struct payload *data)
>  {
>      unsigned int i;
>      int rc;
> @@ -1397,7 +1412,25 @@ static int revert_payload(struct payload *data)
>      }
>
>      for ( i = 0; i < data->nfuncs; i++ )
> -        common_livepatch_revert(&data->funcs[i], &data->fstate[i]);
> +    {
> +        const struct livepatch_func *func = &data->funcs[i];
> +        struct livepatch_fstate *state = &data->fstate[i];
> +
> +        /*
> +         * If the apply action hasn't been executed on this function, do
> +         * nothing.
> +         */
> +        if ( !func->old_addr || state->applied == LIVEPATCH_FUNC_NOT_APPLIED 
> )
> +        {
> +            printk(XENLOG_WARNING LIVEPATCH
> +                   "%s: %s has not been applied before\n",
> +                   __func__, func->name);
> +            continue;
> +        }
> +
> +        arch_livepatch_revert(func, state);
> +        state->applied = LIVEPATCH_FUNC_NOT_APPLIED;
> +    }
>
>      /*
>       * Since we are running with IRQs disabled and the hooks may call common
> @@ -1415,7 +1448,7 @@ static int revert_payload(struct payload *data)
>      return 0;
>  }
>
> -static inline void revert_payload_tail(struct payload *data)
> +void revert_payload_tail(struct payload *data)
>  {
>      list_del(&data->applied_list);
>
> diff --git a/xen/include/xen/livepatch.h b/xen/include/xen/livepatch.h
> index ad0eae28bd0d..d074a5bebecc 100644
> --- a/xen/include/xen/livepatch.h
> +++ b/xen/include/xen/livepatch.h
> @@ -138,35 +138,11 @@ void arch_livepatch_post_action(void);
>  void arch_livepatch_mask(void);
>  void arch_livepatch_unmask(void);
>
> -static inline void common_livepatch_apply(const struct livepatch_func *func,
> -                                          struct livepatch_fstate *state)
> -{
> -    /* If the action has been already executed on this function, do nothing. 
> */
> -    if ( state->applied == LIVEPATCH_FUNC_APPLIED )
> -    {
> -        printk(XENLOG_WARNING LIVEPATCH "%s: %s has been already applied 
> before\n",
> -                __func__, func->name);
> -        return;
> -    }
> -
> -    arch_livepatch_apply(func, state);
> -    state->applied = LIVEPATCH_FUNC_APPLIED;
> -}
> +/* Only for testing purposes. */
> +struct payload;
> +int revert_payload(struct payload *data);
> +void revert_payload_tail(struct payload *data);
>
> -static inline void common_livepatch_revert(const struct livepatch_func *func,
> -                                           struct livepatch_fstate *state)
> -{
> -    /* If the apply action hasn't been executed on this function, do 
> nothing. */
> -    if ( !func->old_addr || state->applied == LIVEPATCH_FUNC_NOT_APPLIED )
> -    {
> -        printk(XENLOG_WARNING LIVEPATCH "%s: %s has not been applied 
> before\n",
> -                __func__, func->name);
> -        return;
> -    }
> -
> -    arch_livepatch_revert(func, state);
> -    state->applied = LIVEPATCH_FUNC_NOT_APPLIED;
> -}
>  #else
>
>  /*
> diff --git a/xen/test/livepatch/xen_action_hooks_norevert.c 
> b/xen/test/livepatch/xen_action_hooks_norevert.c
> index c17385519263..c5fbab174680 100644
> --- a/xen/test/livepatch/xen_action_hooks_norevert.c
> +++ b/xen/test/livepatch/xen_action_hooks_norevert.c
> @@ -96,26 +96,14 @@ static int revert_hook(livepatch_payload_t *payload)
>
>  static void post_revert_hook(livepatch_payload_t *payload)
>  {
> -    int i;
> +    unsigned long flags;
>
>      printk(KERN_DEBUG "%s: Hook starting.\n", __func__);
>
> -    for (i = 0; i < payload->nfuncs; i++)
> -    {
> -        const struct livepatch_func *func = &payload->funcs[i];
> -        struct livepatch_fstate *fstate = &payload->fstate[i];
> -
> -        BUG_ON(revert_cnt != 1);
> -        BUG_ON(fstate->applied != LIVEPATCH_FUNC_APPLIED);
> -
> -        /* Outside of quiesce zone: MAY TRIGGER HOST CRASH/UNDEFINED 
> BEHAVIOR */
> -        arch_livepatch_quiesce();
> -        common_livepatch_revert(payload);
> -        arch_livepatch_revive();
> -        BUG_ON(fstate->applied == LIVEPATCH_FUNC_APPLIED);
> -
> -        printk(KERN_DEBUG "%s: post reverted: %s\n", __func__, func->name);
> -    }
> +    local_irq_save(flags);
> +    BUG_ON(revert_payload(payload));
> +    revert_payload_tail(payload);
> +    local_irq_restore(flags);
>
>      printk(KERN_DEBUG "%s: Hook done.\n", __func__);
>  }
> --
> 2.44.0
>

Reviewed-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>