On Thu, Oct 22, 2026 at 01:57:06AM +0000, Alexei Starovoitov wrote: > From: Alexei Starovoitov <[email protected]> > > 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 <[email protected]>
nice, great there's simple fix for that Acked-by: Jiri Olsa <[email protected]> thanks, jirka > --- > arch/x86/kernel/uprobes.c | 14 ++++++++++++++ > 1 file changed, 14 insertions(+) > > diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c > index 65a2de82ecd2..62bbe41c6466 100644 > --- a/arch/x86/kernel/uprobes.c > +++ b/arch/x86/kernel/uprobes.c > @@ -896,6 +896,9 @@ static int verify_insn(struct page *page, unsigned long > vaddr, uprobe_opcode_t * > case EXPECT_OPTIMIZED: > if (is_opt_insns(&old_opcode[0])) > return 1; > + /* An earlier attempt got this far and failed, nothing to > write. */ > + if (is_swbp_opt_insns(&old_opcode[0])) > + return 0; > break; > case EXPECT_SWBP_OPTIMIZED: > if (is_swbp_opt_insns(&old_opcode[0])) > @@ -1109,6 +1112,17 @@ static bool __is_optimized(struct mm_struct *mm, > uprobe_opcode_t *insn, unsigned > s32 raddr; > } *call = (struct __arch_relative_insn *)(insn + LEA_INSN_SIZE); > > + /* > + * INT3 followed by the rest of the optimized instructions is what is > + * left if int3_update_optimize() or int3_update_unoptimize() failed > + * half-way. It works as a breakpoint, but to restore the original > + * instruction it has to be unoptimized like a completely optimized one. > + * The same has to be done if a debugger has put its INT3 on top of an > + * optimized uprobe. The trampoline can be gone already, so do not look > + * at the target of the call. > + */ > + if (is_swbp_opt_insns(insn)) > + return true; > if (!is_opt_insns(insn)) > return false; > return __in_uprobe_trampoline(mm, vaddr + OPT_INSN_SIZE + call->raddr); > -- > 2.55.0 >
