On Thu, May 15, 2025 at 5:13 AM Jiri Olsa <jo...@kernel.org> wrote:
>
> Adding support to add special mapping for user space trampoline with
> following functions:
>
> uprobe_trampoline_get - find or add uprobe_trampoline
> uprobe_trampoline_put - remove or destroy uprobe_trampoline
>
> The user space trampoline is exported as arch specific user space special
> mapping through tramp_mapping, which is initialized in following changes
> with new uprobe syscall.
>
> The uprobe trampoline needs to be callable/reachable from the probed address,
> so while searching for available address we use is_reachable_by_call function
> to decide if the uprobe trampoline is callable from the probe address.
>
> All uprobe_trampoline objects are stored in uprobes_state object and are
> cleaned up when the process mm_struct goes down. Adding new arch hooks
> for that, because this change is x86_64 specific.
>
> Locking is provided by callers in following changes.
>
> Signed-off-by: Jiri Olsa <jo...@kernel.org>
> ---
> arch/x86/kernel/uprobes.c | 115 ++++++++++++++++++++++++++++++++++++++
> include/linux/uprobes.h | 6 ++
> kernel/events/uprobes.c | 10 ++++
> kernel/fork.c | 1 +
> 4 files changed, 132 insertions(+)
>
[...]
> +static unsigned long find_nearest_page(unsigned long vaddr)
> +{
> + struct vm_unmapped_area_info info = {
> + .length = PAGE_SIZE,
> + .align_mask = ~PAGE_MASK,
> + .flags = VM_UNMAPPED_AREA_TOPDOWN,
> + .low_limit = 0,
would this, technically, allow to allocate memory at NULL (0x0000)
address? should this start at PAGE_SIZE?
> + .high_limit = ULONG_MAX,
> + };
> + unsigned long limit, call_end = vaddr + 5;
> +
> + if (!check_add_overflow(call_end, INT_MIN, &limit))
> + info.low_limit = limit;
> + if (!check_add_overflow(call_end, INT_MAX, &limit))
> + info.high_limit = limit;
> + return vm_unmapped_area(&info);
> +}
[...]
