From: "Gregory Price (Meta)" <gourry@gourry.net>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: bpf@vger.kernel.org, daniel@iogearbox.net, andrii@kernel.org,
eddyz87@gmail.com, memxor@gmail.com, oleg@redhat.com,
peterz@infradead.org, mhiramat@kernel.org, jolsa@kernel.org,
akpm@linux-foundation.org, liam@infradead.org, ljs@kernel.org,
surenb@google.com, david@kernel.org, vbabka@kernel.org,
jannh@google.com, hughd@google.com, kees@kernel.org,
mingo@redhat.com, tglx@kernel.org, x86@kernel.org,
linux-trace-kernel@vger.kernel.org, linux-mm@kvack.org,
linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH bpf-next 3/9] uprobes/x86: Finish an unoptimization which failed half-way
Date: Wed, 21 Oct 2026 22:57:26 -0400 [thread overview]
Message-ID: <179263784614.2549665.557126403507804820.b4-reply@b4> (raw)
In-Reply-To: <20261022015712.1297331-4-alexei.starovoitov@gmail.com>
On 2026-10-22 01:57 +0000, Alexei Starovoitov wrote:
> From: Alexei Starovoitov <ast@kernel.org>
>
> int3_update_unoptimize() restores optimized nop10 in three writes:
>
> 48 8d 64 24 80 e8 d0 d1 d2 d3 lea -0x80(%rsp),%rsp; call tramp
> cc 8d 64 24 80 e8 d0 d1 d2 d3 1. trap new entries
> cc 2e 0f 1f 84 e8 d0 d1 d2 d3 2. restore bytes 1..4
> 66 2e 0f 1f 84 e8 d0 d1 d2 d3 3. restore byte 0
>
> uprobe_write() can fail with -ENOMEM, or with -EINTR when the task is being
> killed. When the 2nd write fails the result of the 1st one stays. Byte 0 is
> a breakpoint and it works. But the next set_orig_insn() doesn't find lea in
> byte 0, takes it for a plain breakpoint and restores one byte:
>
> 66 8d 64 24 80 e8 d0 d1 d2 d3 lea -0x80(%rsp),%sp; call tramp
>
> Nothing recognizes these bytes anymore. The process keeps the call into
> uprobe trampoline, which can be unmapped already.
>
> Teach is_optimized() to recognize the half-way state, and let the 1st write
> of int3_update_unoptimize() skip what is already done.
>
> The failure wasn't reproduced, but the state can be made by hand. Attach to
> nop10, call it to get it optimized, write 0xcc over byte 0, detach.
>
> "uprobes: Don't sleep on mmap_lock under dup_mmap_sem" needs this. There
> fork() removes the breakpoint from its mm. When fork() is killed in
> the middle register_for_each_vma() removes it for the second time.
>
> Fixes: 554ba38456da ("uprobes/x86: Move optimized uprobe from nop5 to nop10")
> Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This was a nice read.
Reviewed-by: Gregory Price (Meta) <gourry@gourry.net>
--
Gregory Price (Meta) <gourry@gourry.net>
next prev parent reply other threads:[~2026-10-22 2:57 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-22 1:57 [PATCH bpf-next 0/9] uprobes: Don't stall fork() when mmap_lock is busy Alexei Starovoitov
2026-10-22 1:57 ` [PATCH bpf-next 1/9] mm: Bring back mmap_write_trylock() Alexei Starovoitov
2026-10-22 1:57 ` [PATCH bpf-next 2/9] uprobes: Don't run exit_mmap() under dup_mmap_sem Alexei Starovoitov
2026-10-22 1:57 ` [PATCH bpf-next 3/9] uprobes/x86: Finish an unoptimization which failed half-way Alexei Starovoitov
2026-10-22 2:57 ` Gregory Price (Meta) [this message]
2026-10-23 7:13 ` Jiri Olsa
2026-10-22 1:57 ` [PATCH bpf-next 4/9] uprobes/x86: Don't WARN if an optimized probe can't be written Alexei Starovoitov
2026-10-22 2:37 ` bot+bpf-ci
2026-10-22 17:56 ` Jann Horn
2026-10-22 19:33 ` Liam R. Howlett
2026-10-23 14:06 ` Lorenzo Stoakes (ARM)
2026-10-23 7:13 ` Jiri Olsa
2026-10-22 1:57 ` [PATCH bpf-next 5/9] uprobes: Don't sleep on mmap_lock under dup_mmap_sem Alexei Starovoitov
2026-10-22 2:37 ` bot+bpf-ci
2026-10-22 23:11 ` Andrii Nakryiko
2026-10-22 1:57 ` [PATCH bpf-next 6/9] uprobes: Don't sleep on mmap_lock with dup_mmap_sem held in dup_mmap() Alexei Starovoitov
2026-10-22 18:42 ` Jann Horn
2026-10-23 20:51 ` David Hildenbrand (Arm)
2026-10-27 15:38 ` Lorenzo Stoakes (ARM)
2026-10-22 1:57 ` [PATCH bpf-next 7/9] fork: Let the new task point to its mm before uprobes can find it Alexei Starovoitov
2026-10-27 16:08 ` Lorenzo Stoakes (ARM)
2026-10-22 1:57 ` [PATCH bpf-next 8/9] uprobes: Don't leak the breakpoints if the unregistering task is killed Alexei Starovoitov
2026-10-22 1:57 ` [PATCH bpf-next 9/9] selftests/bpf: Test uprobes and fork() with busy mmap_lock Alexei Starovoitov
2026-10-22 2:37 ` bot+bpf-ci
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