On 02/28, Sasha Levin wrote: > > The patch below does not apply to the 6.18-stable tree. > If someone wants it applied there, or to any other stable or longterm > tree, then please email the backport, including the original git commit > id to <[email protected]>.
I never know how to react to "failed to apply to stabe" emails. I am going to send [PATCH 6.18.y] in reply to this email. Is it OK? Oleg. > Thanks, > Sasha > > ------------------ original commit in Linus's tree ------------------ > > From d55c571e4333fac71826e8db3b9753fadfbead6a Mon Sep 17 00:00:00 2001 > From: Oleg Nesterov <[email protected]> > Date: Sun, 11 Jan 2026 16:00:37 +0100 > Subject: [PATCH] x86/uprobes: Fix XOL allocation failure for 32-bit tasks > > This script > > #!/usr/bin/bash > > echo 0 > /proc/sys/kernel/randomize_va_space > > echo 'void main(void) {}' > TEST.c > > # -fcf-protection to ensure that the 1st endbr32 insn can't be emulated > gcc -m32 -fcf-protection=branch TEST.c -o test > > bpftrace -e 'uprobe:./test:main {}' -c ./test > > "hangs", the probed ./test task enters an endless loop. > > The problem is that with randomize_va_space == 0 > get_unmapped_area(TASK_SIZE - PAGE_SIZE) called by xol_add_vma() can not > just return the "addr == TASK_SIZE - PAGE_SIZE" hint, this addr is used > by the stack vma. > > arch_get_unmapped_area_topdown() doesn't take TIF_ADDR32 into account and > in_32bit_syscall() is false, this leads to info.high_limit > TASK_SIZE. > vm_unmapped_area() happily returns the high address > TASK_SIZE and then > get_unmapped_area() returns -ENOMEM after the "if (addr > TASK_SIZE - len)" > check. > > handle_swbp() doesn't report this failure (probably it should) and silently > restarts the probed insn. Endless loop. > > I think that the right fix should change the x86 get_unmapped_area() paths > to rely on TIF_ADDR32 rather than in_32bit_syscall(). Note also that if > CONFIG_X86_X32_ABI=y, in_x32_syscall() falsely returns true in this case > because ->orig_ax = -1. > > But we need a simple fix for -stable, so this patch just sets TS_COMPAT if > the probed task is 32-bit to make in_ia32_syscall() true. > > Fixes: 1b028f784e8c ("x86/mm: Introduce mmap_compat_base() for 32-bit mmap()") > Reported-by: Paulo Andrade <[email protected]> > Signed-off-by: Oleg Nesterov <[email protected]> > Signed-off-by: Peter Zijlstra (Intel) <[email protected]> > Link: https://lore.kernel.org/all/[email protected]/ > Cc: [email protected] > Link: https://patch.msgid.link/[email protected] > --- > arch/x86/kernel/uprobes.c | 24 ++++++++++++++++++++++++ > include/linux/uprobes.h | 1 + > kernel/events/uprobes.c | 10 +++++++--- > 3 files changed, 32 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c > index 7be8e361ca55b..619dddf54424e 100644 > --- a/arch/x86/kernel/uprobes.c > +++ b/arch/x86/kernel/uprobes.c > @@ -1823,3 +1823,27 @@ bool is_uprobe_at_func_entry(struct pt_regs *regs) > > return false; > } > + > +#ifdef CONFIG_IA32_EMULATION > +unsigned long arch_uprobe_get_xol_area(void) > +{ > + struct thread_info *ti = current_thread_info(); > + unsigned long vaddr; > + > + /* > + * HACK: we are not in a syscall, but x86 get_unmapped_area() paths > + * ignore TIF_ADDR32 and rely on in_32bit_syscall() to calculate > + * vm_unmapped_area_info.high_limit. > + * > + * The #ifdef above doesn't cover the CONFIG_X86_X32_ABI=y case, > + * but in this case in_32bit_syscall() -> in_x32_syscall() always > + * (falsely) returns true because ->orig_ax == -1. > + */ > + if (test_thread_flag(TIF_ADDR32)) > + ti->status |= TS_COMPAT; > + vaddr = get_unmapped_area(NULL, TASK_SIZE - PAGE_SIZE, PAGE_SIZE, 0, 0); > + ti->status &= ~TS_COMPAT; > + > + return vaddr; > +} > +#endif > diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h > index ee3d36eda45dd..f548fea2adec8 100644 > --- a/include/linux/uprobes.h > +++ b/include/linux/uprobes.h > @@ -242,6 +242,7 @@ extern void arch_uprobe_clear_state(struct mm_struct *mm); > extern void arch_uprobe_init_state(struct mm_struct *mm); > extern void handle_syscall_uprobe(struct pt_regs *regs, unsigned long > bp_vaddr); > extern void arch_uprobe_optimize(struct arch_uprobe *auprobe, unsigned long > vaddr); > +extern unsigned long arch_uprobe_get_xol_area(void); > #else /* !CONFIG_UPROBES */ > struct uprobes_state { > }; > diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c > index a7d7d83ca1d78..dfbce021fb027 100644 > --- a/kernel/events/uprobes.c > +++ b/kernel/events/uprobes.c > @@ -1694,6 +1694,12 @@ static const struct vm_special_mapping xol_mapping = { > .mremap = xol_mremap, > }; > > +unsigned long __weak arch_uprobe_get_xol_area(void) > +{ > + /* Try to map as high as possible, this is only a hint. */ > + return get_unmapped_area(NULL, TASK_SIZE - PAGE_SIZE, PAGE_SIZE, 0, 0); > +} > + > /* Slot allocation for XOL */ > static int xol_add_vma(struct mm_struct *mm, struct xol_area *area) > { > @@ -1709,9 +1715,7 @@ static int xol_add_vma(struct mm_struct *mm, struct > xol_area *area) > } > > if (!area->vaddr) { > - /* Try to map as high as possible, this is only a hint. */ > - area->vaddr = get_unmapped_area(NULL, TASK_SIZE - PAGE_SIZE, > - PAGE_SIZE, 0, 0); > + area->vaddr = arch_uprobe_get_xol_area(); > if (IS_ERR_VALUE(area->vaddr)) { > ret = area->vaddr; > goto fail; > -- > 2.51.0 > > > >
