arm64: kprobes: Allow reentering kprobes while single-stepping

Overview

In the Linux kernel, the following vulnerability has been resolved:

arm64: kprobes: Allow reentering kprobes while single-stepping

A kprobe can be hit while another kprobe is in KPROBE_HIT_SS state. This can happen when tracing or perf code runs from the debug exception path while the first kprobe is preparing or executing its out-of-line single-step instruction.

Currently arm64 treats a kprobe hit in KPROBE_HIT_SS as unrecoverable, the same as a hit in KPROBE_REENTER. This is too strict. A hit in KPROBE_HIT_SS is still a one-level reentry and can be handled by saving the current kprobe state and setting up single-step for the new probe, just like reentry from KPROBE_HIT_ACTIVE or KPROBE_HIT_SSDONE.

The truly unrecoverable case is hitting another kprobe while already in KPROBE_REENTER, because the reentry save area has already been consumed.

Move KPROBE_HIT_SS to the recoverable reentry cases and leave KPROBE_REENTER as the unrecoverable nested reentry case.

This change also requires saving saved_irqflag in struct prev_kprobe. When a nested kprobe calls kprobes_save_local_irqflag(), it overwrites kcb->saved_irqflag with the currently masked DAIF value, losing the outer kprobe's original DAIF state. Without this fix, when the outer kprobe's single-step finishes, kprobes_restore_local_irqflag() applies the wrong DAIF mask and leaves interrupts permanently disabled.

Extend struct prev_kprobe with a saved_irqflag field and save/restore it alongside kp and status. This ensures the outer kprobe's original interrupt state is preserved across reentry.

This mirrors the x86 fix in commit 6a5022a56ac3 ("kprobes/x86: Allow to handle reentered kprobe on single-stepping").

Affected

• Linux >= 2dd0e8d2d2a157dbc83295a78336c2217110f2f8 < bb0fe9121aa0824211aafa33c7d0151fd25ddb75
• Linux >= 2dd0e8d2d2a157dbc83295a78336c2217110f2f8 < f96a0606de6bcc8d937b80e6470fd7a174c17e26
• Linux >= 2dd0e8d2d2a157dbc83295a78336c2217110f2f8 < 1f342b3e44c3035a837b53b217d816f7511c0d0a
• Linux >= 2dd0e8d2d2a157dbc83295a78336c2217110f2f8 < c8e84e292ed4cfc199824146da71bb4397b02a1f
• Linux >= 2dd0e8d2d2a157dbc83295a78336c2217110f2f8 < 68774caca799e9695db56d426c69acebd041c2ed
• Linux >= 2dd0e8d2d2a157dbc83295a78336c2217110f2f8 < a21bf9cb893126e8d9730995708d0be5eb167652
• Linux >= 2dd0e8d2d2a157dbc83295a78336c2217110f2f8 < 23f851ac0078a908bf3422d6467ebc1db5828c46
• Linux 4.8

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.