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Message-Id: <20250714162338.0c9e13b530c835f3010b3ff0@kernel.org>
Date: Mon, 14 Jul 2025 16:23:38 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Jiri Olsa <jolsa@...nel.org>
Cc: Oleg Nesterov <oleg@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
Andrii Nakryiko <andrii@...nel.org>, bpf@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
x86@...nel.org, Song Liu <songliubraving@...com>, Yonghong Song
<yhs@...com>, John Fastabend <john.fastabend@...il.com>, Hao Luo
<haoluo@...gle.com>, Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu
<mhiramat@...nel.org>, Alan Maguire <alan.maguire@...cle.com>, David Laight
<David.Laight@...LAB.COM>, Thomas Weißschuh
<thomas@...ch.de>, Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCHv5 perf/core 08/22] uprobes/x86: Add mapping for
optimized uprobe trampolines
On Fri, 11 Jul 2025 10:29:16 +0200
Jiri Olsa <jolsa@...nel.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 <jolsa@...nel.org>
Looks good to me.
Acked-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
Thank you!
> ---
> arch/x86/kernel/uprobes.c | 144 ++++++++++++++++++++++++++++++++++++++
> include/linux/uprobes.h | 6 ++
> kernel/events/uprobes.c | 10 +++
> kernel/fork.c | 1 +
> 4 files changed, 161 insertions(+)
>
> diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
> index 77050e5a4680..6c4dcbdd0c3c 100644
> --- a/arch/x86/kernel/uprobes.c
> +++ b/arch/x86/kernel/uprobes.c
> @@ -608,6 +608,150 @@ static void riprel_post_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
> *sr = utask->autask.saved_scratch_register;
> }
> }
> +
> +static int tramp_mremap(const struct vm_special_mapping *sm, struct vm_area_struct *new_vma)
> +{
> + return -EPERM;
> +}
> +
> +static struct page *tramp_mapping_pages[2] __ro_after_init;
> +
> +static struct vm_special_mapping tramp_mapping = {
> + .name = "[uprobes-trampoline]",
> + .mremap = tramp_mremap,
> + .pages = tramp_mapping_pages,
> +};
> +
> +struct uprobe_trampoline {
> + struct hlist_node node;
> + unsigned long vaddr;
> +};
> +
> +static bool is_reachable_by_call(unsigned long vtramp, unsigned long vaddr)
> +{
> + long delta = (long)(vaddr + 5 - vtramp);
> +
> + return delta >= INT_MIN && delta <= INT_MAX;
> +}
> +
> +static unsigned long find_nearest_trampoline(unsigned long vaddr)
> +{
> + struct vm_unmapped_area_info info = {
> + .length = PAGE_SIZE,
> + .align_mask = ~PAGE_MASK,
> + };
> + unsigned long low_limit, high_limit;
> + unsigned long low_tramp, high_tramp;
> + unsigned long call_end = vaddr + 5;
> +
> + if (check_add_overflow(call_end, INT_MIN, &low_limit))
> + low_limit = PAGE_SIZE;
> +
> + high_limit = call_end + INT_MAX;
> +
> + /* Search up from the caller address. */
> + info.low_limit = call_end;
> + info.high_limit = min(high_limit, TASK_SIZE);
> + high_tramp = vm_unmapped_area(&info);
> +
> + /* Search down from the caller address. */
> + info.low_limit = max(low_limit, PAGE_SIZE);
> + info.high_limit = call_end;
> + info.flags = VM_UNMAPPED_AREA_TOPDOWN;
> + low_tramp = vm_unmapped_area(&info);
> +
> + if (IS_ERR_VALUE(high_tramp) && IS_ERR_VALUE(low_tramp))
> + return -ENOMEM;
> + if (IS_ERR_VALUE(high_tramp))
> + return low_tramp;
> + if (IS_ERR_VALUE(low_tramp))
> + return high_tramp;
> +
> + /* Return address that's closest to the caller address. */
> + if (call_end - low_tramp < high_tramp - call_end)
> + return low_tramp;
> + return high_tramp;
> +}
> +
> +static struct uprobe_trampoline *create_uprobe_trampoline(unsigned long vaddr)
> +{
> + struct pt_regs *regs = task_pt_regs(current);
> + struct mm_struct *mm = current->mm;
> + struct uprobe_trampoline *tramp;
> + struct vm_area_struct *vma;
> +
> + if (!user_64bit_mode(regs))
> + return NULL;
> +
> + vaddr = find_nearest_trampoline(vaddr);
> + if (IS_ERR_VALUE(vaddr))
> + return NULL;
> +
> + tramp = kzalloc(sizeof(*tramp), GFP_KERNEL);
> + if (unlikely(!tramp))
> + return NULL;
> +
> + tramp->vaddr = vaddr;
> + vma = _install_special_mapping(mm, tramp->vaddr, PAGE_SIZE,
> + VM_READ|VM_EXEC|VM_MAYEXEC|VM_MAYREAD|VM_DONTCOPY|VM_IO,
> + &tramp_mapping);
> + if (IS_ERR(vma)) {
> + kfree(tramp);
> + return NULL;
> + }
> + return tramp;
> +}
> +
> +__maybe_unused
> +static struct uprobe_trampoline *get_uprobe_trampoline(unsigned long vaddr, bool *new)
> +{
> + struct uprobes_state *state = ¤t->mm->uprobes_state;
> + struct uprobe_trampoline *tramp = NULL;
> +
> + if (vaddr > TASK_SIZE || vaddr < PAGE_SIZE)
> + return NULL;
> +
> + hlist_for_each_entry(tramp, &state->head_tramps, node) {
> + if (is_reachable_by_call(tramp->vaddr, vaddr)) {
> + *new = false;
> + return tramp;
> + }
> + }
> +
> + tramp = create_uprobe_trampoline(vaddr);
> + if (!tramp)
> + return NULL;
> +
> + *new = true;
> + hlist_add_head(&tramp->node, &state->head_tramps);
> + return tramp;
> +}
> +
> +static void destroy_uprobe_trampoline(struct uprobe_trampoline *tramp)
> +{
> + /*
> + * We do not unmap and release uprobe trampoline page itself,
> + * because there's no easy way to make sure none of the threads
> + * is still inside the trampoline.
> + */
> + hlist_del(&tramp->node);
> + kfree(tramp);
> +}
> +
> +void arch_uprobe_init_state(struct mm_struct *mm)
> +{
> + INIT_HLIST_HEAD(&mm->uprobes_state.head_tramps);
> +}
> +
> +void arch_uprobe_clear_state(struct mm_struct *mm)
> +{
> + struct uprobes_state *state = &mm->uprobes_state;
> + struct uprobe_trampoline *tramp;
> + struct hlist_node *n;
> +
> + hlist_for_each_entry_safe(tramp, n, &state->head_tramps, node)
> + destroy_uprobe_trampoline(tramp);
> +}
> #else /* 32-bit: */
> /*
> * No RIP-relative addressing on 32-bit
> diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
> index 5080619560d4..b40d33aae016 100644
> --- a/include/linux/uprobes.h
> +++ b/include/linux/uprobes.h
> @@ -17,6 +17,7 @@
> #include <linux/wait.h>
> #include <linux/timer.h>
> #include <linux/seqlock.h>
> +#include <linux/mutex.h>
>
> struct uprobe;
> struct vm_area_struct;
> @@ -185,6 +186,9 @@ struct xol_area;
>
> struct uprobes_state {
> struct xol_area *xol_area;
> +#ifdef CONFIG_X86_64
> + struct hlist_head head_tramps;
> +#endif
> };
>
> typedef int (*uprobe_write_verify_t)(struct page *page, unsigned long vaddr,
> @@ -233,6 +237,8 @@ extern void uprobe_handle_trampoline(struct pt_regs *regs);
> extern void *arch_uretprobe_trampoline(unsigned long *psize);
> extern unsigned long uprobe_get_trampoline_vaddr(void);
> extern void uprobe_copy_from_page(struct page *page, unsigned long vaddr, void *dst, int len);
> +extern void arch_uprobe_clear_state(struct mm_struct *mm);
> +extern void arch_uprobe_init_state(struct mm_struct *mm);
> #else /* !CONFIG_UPROBES */
> struct uprobes_state {
> };
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 6795b8d82b9c..acec91a676b7 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -1802,6 +1802,14 @@ static struct xol_area *get_xol_area(void)
> return area;
> }
>
> +void __weak arch_uprobe_clear_state(struct mm_struct *mm)
> +{
> +}
> +
> +void __weak arch_uprobe_init_state(struct mm_struct *mm)
> +{
> +}
> +
> /*
> * uprobe_clear_state - Free the area allocated for slots.
> */
> @@ -1813,6 +1821,8 @@ void uprobe_clear_state(struct mm_struct *mm)
> delayed_uprobe_remove(NULL, mm);
> mutex_unlock(&delayed_uprobe_lock);
>
> + arch_uprobe_clear_state(mm);
> +
> if (!area)
> return;
>
> diff --git a/kernel/fork.c b/kernel/fork.c
> index bd8c21d64746..70f2d4e2e8fe 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -1009,6 +1009,7 @@ static void mm_init_uprobes_state(struct mm_struct *mm)
> {
> #ifdef CONFIG_UPROBES
> mm->uprobes_state.xol_area = NULL;
> + arch_uprobe_init_state(mm);
> #endif
> }
>
> --
> 2.50.0
>
--
Masami Hiramatsu (Google) <mhiramat@...nel.org>
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