The patch below does not apply to the 6.6-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]>.
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
