From e3cf20e5c68df604315ab30bdbe15dc8a5da556b Mon Sep 17 00:00:00 2001 From: Ard Biesheuvel Date: Tue, 4 Jun 2024 22:32:34 +0100 Subject: [PATCH] ARM: 9405/1: ftrace: Don't assume stack frames are contiguous in memory MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The frame pointer unwinder relies on a standard layout of the stack frame, consisting of (in downward order) Calling frame: PC <---------+ LR | SP | FP | .. locals .. | Callee frame: | PC | LR | SP | FP ----------+ where after storing its previous value on the stack, FP is made to point at the location of PC in the callee stack frame, using the canonical prologue: mov ip, sp stmdb sp!, {fp, ip, lr, pc} sub fp, ip, #4 The ftrace code assumes that this activation record is pushed first, and that any stack space for locals is allocated below this. Strict adherence to this would imply that the caller's value of SP at the time of the function call can always be obtained by adding 4 to FP (which points to PC in the callee frame). However, recent versions of GCC appear to deviate from this rule, and so the only reliable way to obtain the caller's value of SP is to read it from the activation record. Since this involves a read from memory rather than simple arithmetic, we need to use the uaccess API here which protects against inadvertent data aborts resulting from attempts to dereference bogus FP values. The plain uaccess API is ftrace instrumented itself, so to avoid unbounded recursion, use the __get_kernel_nofault() primitive directly. Closes: https://lore.kernel.org/all/alp44tukzo6mvcwl4ke4ehhmojrqnv6xfcdeuliybxfjfvgd3e@gpjvwj33cc76 Closes: https://lore.kernel.org/all/d870c149-4363-43de-b0ea-7125dec5608e@broadcom.com/ Reported-by: Uwe Kleine-König Reported-by: Justin Chen Tested-by: Thorsten Scherer Reviewed-by: Linus Walleij Signed-off-by: Ard Biesheuvel Signed-off-by: Russell King (Oracle) --- arch/arm/kernel/ftrace.c | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-) diff --git a/arch/arm/kernel/ftrace.c b/arch/arm/kernel/ftrace.c index a0b6d1e3812f..e61591f33a6c 100644 --- a/arch/arm/kernel/ftrace.c +++ b/arch/arm/kernel/ftrace.c @@ -232,11 +232,24 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr, unsigned long old; if (unlikely(atomic_read(¤t->tracing_graph_pause))) +err_out: return; if (IS_ENABLED(CONFIG_UNWINDER_FRAME_POINTER)) { - /* FP points one word below parent's top of stack */ - frame_pointer += 4; + /* + * Usually, the stack frames are contiguous in memory but cases + * have been observed where the next stack frame does not live + * at 'frame_pointer + 4' as this code used to assume. + * + * Instead, dereference the field in the stack frame that + * stores the SP of the calling frame: to avoid unbounded + * recursion, this cannot involve any ftrace instrumented + * functions, so use the __get_kernel_nofault() primitive + * directly. + */ + __get_kernel_nofault(&frame_pointer, + (unsigned long *)(frame_pointer - 8), + unsigned long, err_out); } else { struct stackframe frame = { .fp = frame_pointer,