From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5849953381; Wed, 8 May 2024 21:26:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1715203581; cv=none; b=MqVSaG6Z/bJfw1RSyJ6a25HdJchgu8gYaVnhjISu4G4Y9xbYFdvJkM7dPln5By7ZDjAJogGz5FFgD9v6QYlUdbhTzwTlV6xG+eBlS069bSCPGKccmNt7bgfNcgI4ZryOSzXMZ+ZA3hKmL+88mq2ZEfGGdMaIUbTV4c57uQeJgTo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1715203581; c=relaxed/simple; bh=IcCH6HvV+fA+Q/OECgPQYvioKi/QPVoGcj2BlQkwI7Y=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Id5lakDuorL/Xy3l5Lir9CO/EMR99PbJpMI2DK2vSZsZxU45RFVrbu3fW4KJP3OJgILg5zAR/cV8nyCU/8OxvxvGijODL5el0ZMFuNiDzmlQgQkli8ygvkRV9h6diRrfq6LrUgZFYgX+2tmKdrL1DVXAb734UdPJZWqIPcJpTXU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=sw8hzS/a; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="sw8hzS/a" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B82DDC113CC; Wed, 8 May 2024 21:26:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1715203580; bh=IcCH6HvV+fA+Q/OECgPQYvioKi/QPVoGcj2BlQkwI7Y=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=sw8hzS/adU8d5M49o6DylDQlNAy9IE+DtQDm5jWqYvG7O4mMwdyZz4EKdKi9E93zR Lw7owf95gWNLBHPXw/zf57BpK1qRNiUuke0Ce/mtm8TdbtJ8c1OTD420XGyiW0QgQS +g+/MH2MuIjvoec2TAnxliVuiuZoroh+lDTf+DxNdvU6wC4MmHTEXhBLYjJkFIX4F1 Ez6B6tGcijvmG/c8nJwCzrDYE452FU42AoHB8RNfhwOOgxPgx6TKy7O1rbDPhz8c3M t2VQYosBxFJGJzV836P1KVzPLFE0jZm3tPS7JEE+EnEFixk4czjCrj4XSs1YreuAd8 MNiD3rZsRalsA== From: Andrii Nakryiko To: linux-trace-kernel@vger.kernel.org, rostedt@goodmis.org, mhiramat@kernel.org Cc: x86@kernel.org, peterz@infradead.org, mingo@redhat.com, tglx@linutronix.de, bpf@vger.kernel.org, rihams@fb.com, linux-perf-users@vger.kernel.org, Andrii Nakryiko Subject: [PATCH 3/4] perf,x86: avoid missing caller address in stack traces captured in uprobe Date: Wed, 8 May 2024 14:26:04 -0700 Message-ID: <20240508212605.4012172-4-andrii@kernel.org> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20240508212605.4012172-1-andrii@kernel.org> References: <20240508212605.4012172-1-andrii@kernel.org> Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit When tracing user functions with uprobe functionality, it's common to install the probe (e.g., a BPF program) at the first instruction of the function. This is often going to be `push %rbp` instruction in function preamble, which means that within that function frame pointer hasn't been established yet. This leads to consistently missing an actual caller of the traced function, because perf_callchain_user() only records current IP (capturing traced function) and then following frame pointer chain (which would be caller's frame, containing the address of caller's caller). So when we have target_1 -> target_2 -> target_3 call chain and we are tracing an entry to target_3, captured stack trace will report target_1 -> target_3 call chain, which is wrong and confusing. This patch proposes a x86-64-specific heuristic to detect `push %rbp` instruction being traced. If that's the case, with the assumption that applicatoin is compiled with frame pointers, this instruction would be a strong indicator that this is the entry to the function. In that case, return address is still pointed to by %rsp, so we fetch it and add to stack trace before proceeding to unwind the rest using frame pointer-based logic. Signed-off-by: Andrii Nakryiko --- arch/x86/events/core.c | 20 ++++++++++++++++++++ include/linux/uprobes.h | 2 ++ kernel/events/uprobes.c | 2 ++ 3 files changed, 24 insertions(+) diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c index 5b0dd07b1ef1..82d5570b58ff 100644 --- a/arch/x86/events/core.c +++ b/arch/x86/events/core.c @@ -2884,6 +2884,26 @@ perf_callchain_user(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs return; pagefault_disable(); + +#ifdef CONFIG_UPROBES + /* + * If we are called from uprobe handler, and we are indeed at the very + * entry to user function (which is normally a `push %rbp` instruction, + * under assumption of application being compiled with frame pointers), + * we should read return address from *regs->sp before proceeding + * to follow frame pointers, otherwise we'll skip immediate caller + * as %rbp is not yet setup. + */ + if (current->utask) { + struct arch_uprobe *auprobe = current->utask->auprobe; + u64 ret_addr; + + if (auprobe && auprobe->insn[0] == 0x55 /* push %rbp */ && + !__get_user(ret_addr, (const u64 __user *)regs->sp)) + perf_callchain_store(entry, ret_addr); + } +#endif + while (entry->nr < entry->max_stack) { if (!valid_user_frame(fp, sizeof(frame))) break; diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h index 0c57eec85339..7b785cd30d86 100644 --- a/include/linux/uprobes.h +++ b/include/linux/uprobes.h @@ -76,6 +76,8 @@ struct uprobe_task { struct uprobe *active_uprobe; unsigned long xol_vaddr; + struct arch_uprobe *auprobe; + struct return_instance *return_instances; unsigned int depth; }; diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c index 1c99380dc89d..504693845187 100644 --- a/kernel/events/uprobes.c +++ b/kernel/events/uprobes.c @@ -2072,6 +2072,7 @@ static void handler_chain(struct uprobe *uprobe, struct pt_regs *regs) bool need_prep = false; /* prepare return uprobe, when needed */ down_read(&uprobe->register_rwsem); + current->utask->auprobe = &uprobe->arch; for (uc = uprobe->consumers; uc; uc = uc->next) { int rc = 0; @@ -2086,6 +2087,7 @@ static void handler_chain(struct uprobe *uprobe, struct pt_regs *regs) remove &= rc; } + current->utask->auprobe = NULL; if (need_prep && !remove) prepare_uretprobe(uprobe, regs); /* put bp at return */ -- 2.43.0