From: Mark Rutland <mark.rutland@arm.com> mainline inclusion from mainline-v6.13-rc3 commit 65ac33bed8b9255213b08ed153dbe9c0ca3535e6 category: bugfix bugzilla: https://atomgit.com/openeuler/kernel/issues/9572 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... -------------------------------- The arm64 stacktrace code has a few error conditions where a WARN_ON_ONCE() is triggered before the stacktrace is terminated and an error is returned to the caller. The conditions shouldn't be triggered when unwinding the current task, but it is possible to trigger these when unwinding another task which is not blocked, as the stack of that task is concurrently modified. Kent reports that these warnings can be triggered while running filesystem tests on bcachefs, which calls the stacktrace code directly. To produce a meaningful stacktrace of another task, the task in question should be blocked, but the stacktrace code is expected to be robust to cases where it is not blocked. Note that this is purely about not unuduly scaring the user and/or crashing the kernel; stacktraces in such cases are meaningless and may leak kernel secrets from the stack of the task being unwound. Ideally we'd pin the task in a blocked state during the unwind, as we do for /proc/${PID}/wchan since commit: 42a20f86dc19f928 ("sched: Add wrapper for get_wchan() to keep task blocked") ... but a bunch of places don't do that, notably /proc/${PID}/stack, where we don't pin the task in a blocked state, but do restrict the output to privileged users since commit: f8a00cef17206ecd ("proc: restrict kernel stack dumps to root") ... and so it's possible to trigger these warnings accidentally, e.g. by reading /proc/*/stack (as root): | for n in $(seq 1 10); do | while true; do cat /proc/*/stack > /dev/null 2>&1; done & | done | ------------[ cut here ]------------ | WARNING: CPU: 3 PID: 166 at arch/arm64/kernel/stacktrace.c:207 arch_stack_walk+0x1c8/0x370 | Modules linked in: | CPU: 3 UID: 0 PID: 166 Comm: cat Not tainted 6.13.0-rc2-00003-g3dafa7a7925d #2 | Hardware name: linux,dummy-virt (DT) | pstate: 81400005 (Nzcv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--) | pc : arch_stack_walk+0x1c8/0x370 | lr : arch_stack_walk+0x1b0/0x370 | sp : ffff800080773890 | x29: ffff800080773930 x28: fff0000005c44500 x27: fff00000058fa038 | x26: 000000007ffff000 x25: 0000000000000000 x24: 0000000000000000 | x23: ffffa35a8d9600ec x22: 0000000000000000 x21: fff00000043a33c0 | x20: ffff800080773970 x19: ffffa35a8d960168 x18: 0000000000000000 | x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000 | x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000 | x11: 0000000000000000 x10: 0000000000000000 x9 : 0000000000000000 | x8 : ffff8000807738e0 x7 : ffff8000806e3800 x6 : ffff8000806e3818 | x5 : ffff800080773920 x4 : ffff8000806e4000 x3 : ffff8000807738e0 | x2 : 0000000000000018 x1 : ffff8000806e3800 x0 : 0000000000000000 | Call trace: | arch_stack_walk+0x1c8/0x370 (P) | stack_trace_save_tsk+0x8c/0x108 | proc_pid_stack+0xb0/0x134 | proc_single_show+0x60/0x120 | seq_read_iter+0x104/0x438 | seq_read+0xf8/0x140 | vfs_read+0xc4/0x31c | ksys_read+0x70/0x108 | __arm64_sys_read+0x1c/0x28 | invoke_syscall+0x48/0x104 | el0_svc_common.constprop.0+0x40/0xe0 | do_el0_svc+0x1c/0x28 | el0_svc+0x30/0xcc | el0t_64_sync_handler+0x10c/0x138 | el0t_64_sync+0x198/0x19c | ---[ end trace 0000000000000000 ]--- Fix this by only warning when unwinding the current task. When unwinding another task the error conditions will be handled by returning an error without producing a warning. The two warnings in kunwind_next_frame_record_meta() were added recently as part of commit: c2c6b27b5aa14fa2 ("arm64: stacktrace: unwind exception boundaries") The warning when recovering the fgraph return address has changed form many times, but was originally introduced back in commit: 9f416319f40cd857 ("arm64: fix unwind_frame() for filtered out fn for function graph tracing") Fixes: c2c6b27b5aa1 ("arm64: stacktrace: unwind exception boundaries") Fixes: 9f416319f40c ("arm64: fix unwind_frame() for filtered out fn for function graph tracing") Signed-off-by: Mark Rutland <mark.rutland@arm.com> Reported-by: Kent Overstreet <kent.overstreet@linux.dev> Cc: Kees Cook <keescook@chromium.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Will Deacon <will@kernel.org> Link: https://lore.kernel.org/r/20241211140704.2498712-3-mark.rutland@arm.com Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> Conflicts: arch/arm64/kernel/stacktrace.c [c2c6b27b5aa1 ("arm64: stacktrace: unwind exception boundaries") This commit introduces an unwind-boundary feature that is not required for this backport.] Signed-off-by: Tengda Wu <wutengda2@huawei.com> --- arch/arm64/kernel/stacktrace.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c index 17f66a74c745..80cd45e4a922 100644 --- a/arch/arm64/kernel/stacktrace.c +++ b/arch/arm64/kernel/stacktrace.c @@ -81,8 +81,10 @@ unwind_recover_return_address(struct unwind_state *state) unsigned long orig_pc; orig_pc = ftrace_graph_ret_addr(state->task, NULL, state->pc, (void *)state->fp); - if (WARN_ON_ONCE(state->pc == orig_pc)) + if (state->pc == orig_pc) { + WARN_ON_ONCE(state->task == current); return -EINVAL; + } state->pc = orig_pc; } #endif /* CONFIG_FUNCTION_GRAPH_TRACER */ -- 2.34.1