From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pg1-f202.google.com (mail-pg1-f202.google.com [209.85.215.202]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3E2503655D7 for ; Thu, 16 Jul 2026 07:40:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.215.202 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784187639; cv=none; b=uMt+zsHuK3zd23UoUy6KuaY4EEk7WxA00b2GU5jAyIJQ92/L2qP47zkAi2SCgmLpwfbz5JvkuPuMIGBTtG5Bg/V8izIYFeyAq+CTv6pOf2K48gheOTJL5k1lr62IPft+z1yED75cnO1hdt9CKS0BJKPwMGAZ4aseof7aOJ1PXSc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784187639; c=relaxed/simple; bh=X32jELlMF94Xl0NmY7vypZygDvQes8I0SpcBi7a5U1w=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=VqmuKwtYo/mvRgX2FvYAH32G2w+lVXzH4m2fMfAJJZjSd7UFV5W644W10ww6BmqOzrFC0Bn5JoyBBuF83VfLEd5xO0ZPU6EpENkvUFcwL6j8OYxZPCqfsIc+BT+ss2CyvbCaIaVgZFzE+hhZoJIGFybtF4lpZLFh59OByniJiCU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--irogers.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=bXcp7yiv; arc=none smtp.client-ip=209.85.215.202 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--irogers.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="bXcp7yiv" Received: by mail-pg1-f202.google.com with SMTP id 41be03b00d2f7-c88aab7c1fcso15131750a12.3 for ; Thu, 16 Jul 2026 00:40:34 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1784187632; x=1784792432; darn=vger.kernel.org; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:from:to:cc:subject:date:message-id:reply-to :content-type; bh=yE24h4tZ7G95OOIPOTLF1J84+Ri6r1nt8tkDTfpbhf0=; b=bXcp7yiv1899J+64f+8zwT1x8j3de+epXnrPXG/4WqAG1mQGbOimUmOwadxhfVl2Au M6si6OV48TdszTDbLjNIOy4zsRcV7Qbcq25eH8wknztpcXpG4G3bUuRKiz0bZqOcB9cF 0RYxLQ4dukUAOYMfmBbsTympLTTnZzc4B8FDgTE1Wf+BBwwkJvWEl9DxSTNYiPMp5JrQ sScKW7Pxlin9W7FaM5SxFioaDvN+XVPlNFvqVlfhULF1xkTl+OrcslDiRqAJpnckCtid EH+kdPJsO0CanIJe47yUejVeg9sda7eAAS/jGBmh1WDKf/dL5ri7vPU0pmFXVlKpEDtd tiTg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1784187632; x=1784792432; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to:content-type; bh=yE24h4tZ7G95OOIPOTLF1J84+Ri6r1nt8tkDTfpbhf0=; b=OuQqejYyxT01JWSwHI6tAP6JLccHpGOWF1/zi52FxoiFdrXDlLSF6yVQxBnIi66Rry b6IljnV6nt/qzOtK4rU41Do+dBkNZJmzZMBrA7TEZDJwcgZJIcM+g9u6FpUM+Dr4Gnso AIdtAUEt6qdBgy8Np6FpY10M37NSuiHoDN1V8eZIhF2PjCYZG/kfVNJqnC7jr0nps+/9 qMTiV3RPZ/JDoZQhxvfIRnzezGMc0M6fkRXCnWLJCy1OL2KrO+rivaoVxOgg/C0rB9Pt Jz16R6qmsIbvctAXnFTok0oOrYHPQhHvGC3gL7iZ8jpyZhmRp89/+L6K1+S/rthImDiM /kyQ== X-Forwarded-Encrypted: i=1; AHgh+RoR2T/YU8LLuwWhER5vfNqL9HY1NqUrHdRELV/T6lxgh3PVQ9W3qBMDlPZoRWOt8hAyIhxm8HQnO582EMaSFQMR@vger.kernel.org X-Gm-Message-State: AOJu0YwWUUcPjomLbi3F7a8G8GFXzBpqVux+efI0DCIRafAa268dcRsK WuPymPUBoSdjXtlZO+AS0awVcfDyqKhZJD27Z8EBCWgg7motfDcMyGipNGlVMfNCQQJhCAKmX4S l/51SBwKaRQ== X-Received: from dybrt21.prod.google.com ([2002:a05:7301:4715:b0:313:d566:5bbb]) (user=irogers job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a21:7106:b0:3c3:94bb:ceb3 with SMTP id adf61e73a8af0-3c394bbd03dmr690942637.10.1784187632131; Thu, 16 Jul 2026 00:40:32 -0700 (PDT) Date: Thu, 16 Jul 2026 00:40:28 -0700 In-Reply-To: Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: X-Mailer: git-send-email 2.55.0.141.g00534a21ce-goog Message-ID: <20260716074028.568999-1-irogers@google.com> Subject: [PATCH v2] perf cap: Remove used_root parameter and simplify capability checks From: Ian Rogers To: namhyung@kernel.org, acme@kernel.org Cc: abyssmystery@gmail.com, adrian.hunter@intel.com, irogers@google.com, james.clark@linaro.org, jolsa@kernel.org, linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, mingo@redhat.com, peterz@infradead.org Content-Type: text/plain; charset="UTF-8" Refactor perf_cap__capable() to completely remove the used_root out-parameter as requested by the maintainer. Relying on an explicit used_root boolean poisoned sequential capability checks (e.g. failing CAP_SYS_ADMIN checks poisoning the flag for subsequent CAP_PERFMON evaluations for unprivileged users) and created redundant complexity across check_ftrace_capable(), symbol__read_kptr_restrict(), and perf_event_paranoid_check(). Streamline the capability API to perform a pure true/false boolean evaluation. The function checks the Effective set using SYS_capget; if the syscall is missing or fails on legacy kernels, it cleanly falls back to checking EUID == 0. This perfectly preserves modern capability-aware host sessions, guarantees transparent fallback for older kernels, and correctly rejects privileged operations for containerized root processes that have explicitly dropped their capability bounding and permitted sets. Fixes: e25ebda78e23 ("perf cap: Tidy up and improve capability testing") Suggested-by: Namhyung Kim Assisted-by: Antigravity:gemini-3.5-flash Signed-off-by: Ian Rogers --- tools/perf/builtin-ftrace.c | 13 +++---------- tools/perf/util/bpf-filter.c | 22 +++++++++------------- tools/perf/util/cap.c | 4 +--- tools/perf/util/cap.h | 3 +-- tools/perf/util/symbol.c | 3 +-- tools/perf/util/util.c | 12 +++--------- 6 files changed, 18 insertions(+), 39 deletions(-) diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c index 9e4c5220d43c..f7126196b092 100644 --- a/tools/perf/builtin-ftrace.c +++ b/tools/perf/builtin-ftrace.c @@ -72,18 +72,11 @@ static void ftrace__workload_exec_failed_signal(int signo __maybe_unused, static bool check_ftrace_capable(void) { - bool used_root; - - if (perf_cap__capable(CAP_PERFMON, &used_root)) - return true; - - if (!used_root && perf_cap__capable(CAP_SYS_ADMIN, &used_root)) + if (perf_cap__capable(CAP_PERFMON) || + perf_cap__capable(CAP_SYS_ADMIN)) return true; - pr_err("ftrace only works for %s!\n", - used_root ? "root" - : "users with the CAP_PERFMON or CAP_SYS_ADMIN capability" - ); + pr_err("ftrace only works for users with the CAP_PERFMON or CAP_SYS_ADMIN capability!\n"); return false; } diff --git a/tools/perf/util/bpf-filter.c b/tools/perf/util/bpf-filter.c index 1a2e7b388d57..bcd81084e342 100644 --- a/tools/perf/util/bpf-filter.c +++ b/tools/perf/util/bpf-filter.c @@ -629,24 +629,20 @@ struct perf_bpf_filter_expr *perf_bpf_filter_expr__new(enum perf_bpf_filter_term static bool check_bpf_filter_capable(void) { - bool used_root; + int fd; - if (perf_cap__capable(CAP_BPF, &used_root)) + if (perf_cap__capable(CAP_BPF)) return true; - if (!used_root) { - /* Check if root already pinned the filter programs and maps */ - int fd = get_pinned_fd("filters"); - - if (fd >= 0) { - close(fd); - return true; - } + /* Check if root already pinned the filter programs and maps */ + fd = get_pinned_fd("filters"); + if (fd >= 0) { + close(fd); + return true; } - pr_err("Error: BPF filter only works for %s!\n" - "\tPlease run 'perf record --setup-filter pin' as root first.\n", - used_root ? "root" : "users with the CAP_BPF capability"); + pr_err("Error: BPF filter only works for users with the CAP_BPF capability!\n" + "\tPlease run 'perf record --setup-filter pin' as root first.\n"); return false; } diff --git a/tools/perf/util/cap.c b/tools/perf/util/cap.c index ac6d1d9a523d..272bd8255ff1 100644 --- a/tools/perf/util/cap.c +++ b/tools/perf/util/cap.c @@ -12,7 +12,7 @@ #define MAX_LINUX_CAPABILITY_U32S _LINUX_CAPABILITY_U32S_3 -bool perf_cap__capable(int cap, bool *used_root) +bool perf_cap__capable(int cap) { struct __user_cap_header_struct header = { .version = _LINUX_CAPABILITY_VERSION_3, @@ -21,7 +21,6 @@ bool perf_cap__capable(int cap, bool *used_root) struct __user_cap_data_struct data[MAX_LINUX_CAPABILITY_U32S] = {}; __u32 cap_val; - *used_root = false; while (syscall(SYS_capget, &header, &data[0]) == -1) { /* Retry, first attempt has set the header.version correctly. */ if (errno == EINVAL && header.version != _LINUX_CAPABILITY_VERSION_3 && @@ -29,7 +28,6 @@ bool perf_cap__capable(int cap, bool *used_root) continue; pr_debug2("capget syscall failed (%m) fall back on root check\n"); - *used_root = true; return geteuid() == 0; } diff --git a/tools/perf/util/cap.h b/tools/perf/util/cap.h index c1b8ac033ccc..bf09fb20c779 100644 --- a/tools/perf/util/cap.h +++ b/tools/perf/util/cap.h @@ -18,7 +18,6 @@ #define CAP_BPF 39 #endif -/* Query if a capability is supported, used_root is set if the fallback root check was used. */ -bool perf_cap__capable(int cap, bool *used_root); +bool perf_cap__capable(int cap); #endif /* __PERF_CAP_H */ diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c index a562702b4841..94f9c8faedda 100644 --- a/tools/perf/util/symbol.c +++ b/tools/perf/util/symbol.c @@ -2452,8 +2452,7 @@ static bool symbol__read_kptr_restrict(void) { bool value = false; FILE *fp = fopen("/proc/sys/kernel/kptr_restrict", "r"); - bool used_root; - bool cap_syslog = perf_cap__capable(CAP_SYSLOG, &used_root); + bool cap_syslog = perf_cap__capable(CAP_SYSLOG); if (fp != NULL) { char line[8]; diff --git a/tools/perf/util/util.c b/tools/perf/util/util.c index 2c2a5c449ffd..8f7cd32f524d 100644 --- a/tools/perf/util/util.c +++ b/tools/perf/util/util.c @@ -378,15 +378,9 @@ int perf_event_paranoid(void) bool perf_event_paranoid_check(int max_level) { - bool used_root; - - if (perf_cap__capable(CAP_SYS_ADMIN, &used_root)) - return true; - - if (!used_root && perf_cap__capable(CAP_PERFMON, &used_root)) - return true; - - return perf_event_paranoid() <= max_level; + return perf_cap__capable(CAP_SYS_ADMIN) || + perf_cap__capable(CAP_PERFMON) || + perf_event_paranoid() <= max_level; } int perf_tip(char **strp, const char *dirpath) -- 2.55.0.141.g00534a21ce-goog