sched_ext: Maintain an online cid mask in the scheduler arenagrafted

Schedulers on the default cid mapping treat [0, nr_online_cids) as the
online set and restart on hotplug. Schedulers that install their own mapping
with scx_bpf_cid_override() have no way to learn which cids are online: the
count no longer identifies members and the CPU-form cpumask is unusable from
cid programs. This is an obvious hole in the cid API.

Add scx_bpf_online_cmask(), a kernel-maintained cmask in the scheduler's
arena, allocated alongside the per-CPU scratch masks and populated after the
cid mapping is finalized and before ops.init(), for child schedulers too.
The pointer stays valid through ops.exit() with no reference to take. It is
the arena offset as a void pointer, the same form struct_ops arena arguments
arrive in. The verifier types the void return as a scalar for the program's
arena cast.

The mask follows the SCX hotplug notifications: seeded from cpu_active_mask
and updated before ops.cid_online/offline() runs, so it lags cpu_online_mask
only inside a hotplug transition. Updates walk the scheduler list under the
lock that also serializes unlinking. Reads are live, not atomic snapshots.
Root initialization excludes hotplug.

v2: Reworded the getter kerneldoc (Andrea Righi).

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

22 files changed, 219 insertions, 0 deletions

diff --git a/lib/test_fortify/.gitignore b/lib/test_fortify/.gitignore
new file mode 100644
index 000000000..c1ba37d14
--- /dev/null
+++ b/lib/test_fortify/.gitignore
@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
+/*.log
diff --git a/lib/test_fortify/Makefile b/lib/test_fortify/Makefile
new file mode 100644
index 000000000..44cd5df41
--- /dev/null
+++ b/lib/test_fortify/Makefile
@@ -0,0 +1,26 @@
+# SPDX-License-Identifier: GPL-2.0
+
+ccflags-y := $(call cc-disable-warning,fortify-source)
+ccflags-y += $(call cc-disable-warning,stringop-overread)
+
+quiet_cmd_test_fortify = TEST    $@
+      cmd_test_fortify = $(CONFIG_SHELL) $(src)/test_fortify.sh \
+			$< $@ "$(NM)" $(CC) $(c_flags) -DKBUILD_EXTRA_WARN1
+
+$(obj)/%.log: $(src)/%.c $(src)/test_fortify.sh FORCE
+	$(call if_changed_dep,test_fortify)
+
+logs = $(patsubst $(src)/%.c, %.log, $(wildcard $(src)/*-*.c))
+targets += $(logs)
+
+quiet_cmd_gen_fortify_log = CAT     $@
+      cmd_gen_fortify_log = cat $(or $(real-prereqs),/dev/null) > $@
+
+$(obj)/test_fortify.log: $(addprefix $(obj)/, $(logs)) FORCE
+	$(call if_changed,gen_fortify_log)
+
+always-y += test_fortify.log
+
+# Some architectures define __NO_FORTIFY if __SANITIZE_ADDRESS__ is undefined.
+# Pass CFLAGS_KASAN to avoid warnings.
+KASAN_SANITIZE := y
diff --git a/lib/test_fortify/read_overflow-memchr.c b/lib/test_fortify/read_overflow-memchr.c
new file mode 100644
index 000000000..2743084b3
--- /dev/null
+++ b/lib/test_fortify/read_overflow-memchr.c
@@ -0,0 +1,5 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#define TEST	\
+	memchr(small, 0x7A, sizeof(small) + 1)
+
+#include "test_fortify.h"
diff --git a/lib/test_fortify/read_overflow-memchr_inv.c b/lib/test_fortify/read_overflow-memchr_inv.c
new file mode 100644
index 000000000..b26e1f1bc
--- /dev/null
+++ b/lib/test_fortify/read_overflow-memchr_inv.c
@@ -0,0 +1,5 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#define TEST	\
+	memchr_inv(small, 0x7A, sizeof(small) + 1)
+
+#include "test_fortify.h"
diff --git a/lib/test_fortify/read_overflow-memcmp.c b/lib/test_fortify/read_overflow-memcmp.c
new file mode 100644
index 000000000..d5d301ff6
--- /dev/null
+++ b/lib/test_fortify/read_overflow-memcmp.c
@@ -0,0 +1,5 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#define TEST	\
+	memcmp(small, large, sizeof(small) + 1)
+
+#include "test_fortify.h"
diff --git a/lib/test_fortify/read_overflow-memscan.c b/lib/test_fortify/read_overflow-memscan.c
new file mode 100644
index 000000000..c1a97f2df
--- /dev/null
+++ b/lib/test_fortify/read_overflow-memscan.c
@@ -0,0 +1,5 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#define TEST	\
+	memscan(small, 0x7A, sizeof(small) + 1)
+
+#include "test_fortify.h"
diff --git a/lib/test_fortify/read_overflow2-memcmp.c b/lib/test_fortify/read_overflow2-memcmp.c
new file mode 100644
index 000000000..c6091e640
--- /dev/null
+++ b/lib/test_fortify/read_overflow2-memcmp.c
@@ -0,0 +1,5 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#define TEST	\
+	memcmp(large, small, sizeof(small) + 1)
+
+#include "test_fortify.h"
diff --git a/lib/test_fortify/read_overflow2-memcpy.c b/lib/test_fortify/read_overflow2-memcpy.c
new file mode 100644
index 000000000..07b62e56c
--- /dev/null
+++ b/lib/test_fortify/read_overflow2-memcpy.c
@@ -0,0 +1,5 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#define TEST	\
+	memcpy(large, instance.buf, sizeof(large))
+
+#include "test_fortify.h"
diff --git a/lib/test_fortify/read_overflow2-memmove.c b/lib/test_fortify/read_overflow2-memmove.c
new file mode 100644
index 000000000..34edfab04
--- /dev/null
+++ b/lib/test_fortify/read_overflow2-memmove.c
@@ -0,0 +1,5 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#define TEST	\
+	memmove(large, instance.buf, sizeof(large))
+
+#include "test_fortify.h"
diff --git a/lib/test_fortify/read_overflow2_field-memcpy.c b/lib/test_fortify/read_overflow2_field-memcpy.c
new file mode 100644
index 000000000..de9569266
--- /dev/null
+++ b/lib/test_fortify/read_overflow2_field-memcpy.c
@@ -0,0 +1,5 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#define TEST	\
+	memcpy(large, instance.buf, sizeof(instance.buf) + 1)
+
+#include "test_fortify.h"
diff --git a/lib/test_fortify/read_overflow2_field-memmove.c b/lib/test_fortify/read_overflow2_field-memmove.c
new file mode 100644
index 000000000..6cc2724c8
--- /dev/null
+++ b/lib/test_fortify/read_overflow2_field-memmove.c
@@ -0,0 +1,5 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#define TEST	\
+	memmove(large, instance.buf, sizeof(instance.buf) + 1)
+
+#include "test_fortify.h"
diff --git a/lib/test_fortify/test_fortify.h b/lib/test_fortify/test_fortify.h
new file mode 100644
index 000000000..d22664fff
--- /dev/null
+++ b/lib/test_fortify/test_fortify.h
@@ -0,0 +1,35 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#include <linux/kernel.h>
+#include <linux/printk.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+
+void do_fortify_tests(void);
+
+#define __BUF_SMALL	16
+#define __BUF_LARGE	32
+struct fortify_object {
+	int a;
+	char buf[__BUF_SMALL];
+	int c;
+};
+
+#define LITERAL_SMALL "AAAAAAAAAAAAAAA"
+#define LITERAL_LARGE "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"
+const char small_src[__BUF_SMALL] = LITERAL_SMALL;
+const char large_src[__BUF_LARGE] = LITERAL_LARGE;
+
+char small[__BUF_SMALL];
+char large[__BUF_LARGE];
+struct fortify_object instance;
+size_t size;
+
+void do_fortify_tests(void)
+{
+	/* Normal initializations. */
+	memset(&instance, 0x32, sizeof(instance));
+	memset(small, 0xA5, sizeof(small));
+	memset(large, 0x5A, sizeof(large));
+
+	TEST;
+}
diff --git a/lib/test_fortify/test_fortify.sh b/lib/test_fortify/test_fortify.sh
new file mode 100644
index 000000000..ad6dd44fa
--- /dev/null
+++ b/lib/test_fortify/test_fortify.sh
@@ -0,0 +1,66 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-only
+set -e
+
+# Argument 1: Source file to build.
+IN="$1"
+shift
+# Extract just the filename for error messages below.
+FILE="${IN##*/}"
+# Extract the function name for error messages below.
+FUNC="${FILE#*-}"
+FUNC="${FUNC%%-*}"
+FUNC="${FUNC%%.*}"
+# Extract the symbol to test for in build/symbol test below.
+WANT="__${FILE%%-*}"
+
+# Argument 2: Where to write the build log.
+OUT="$1"
+shift
+TMP="${OUT%/*}/.${OUT##*/}.tmp"
+
+# Argument 3: Path to "nm" tool.
+NM="$1"
+shift
+
+# Remaining arguments are: $(CC) $(c_flags)
+
+# Clean up temporary file at exit.
+__cleanup() {
+	rm -f "$TMP"
+}
+trap __cleanup EXIT HUP INT QUIT TERM
+
+# Function names in warnings are wrapped in backticks under UTF-8 locales.
+# Run the commands with LANG=C so that grep output will not change.
+export LANG=C
+
+status=
+# Attempt to build a source that is expected to fail with a specific warning.
+if "$@" -Werror -c "$IN" -o "$OUT".o 2> "$TMP" ; then
+	# If the build succeeds, either the test has failed or the
+	# warning may only happen at link time (Clang). In that case,
+	# make sure the expected symbol is unresolved in the symbol list.
+	# If so, FORTIFY is working for this case.
+	if ! $NM -A "$OUT".o | grep -m1 "\bU ${WANT}$" >>"$TMP" ; then
+		status="warning: unsafe ${FUNC}() usage lacked '$WANT' symbol in $IN"
+	fi
+else
+	# If the build failed, check for the warning in the stderr.
+	# GCC:
+	# ./include/linux/fortify-string.h:316:25: error: call to '__write_overflow_field' declared with attribute warning: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Werror=attribute-warning]
+	# Clang 14:
+	# ./include/linux/fortify-string.h:316:4: error: call to __write_overflow_field declared with 'warning' attribute: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Werror,-Wattribute-warning]
+	if ! grep -Eq -m1 "error: call to .?\b${WANT}\b.?" "$TMP" ; then
+		status="warning: unsafe ${FUNC}() usage lacked '$WANT' warning in $IN"
+	fi
+fi
+
+if [ -n "$status" ]; then
+	# Report on failure results, including compilation warnings.
+	echo "$status" | tee "$OUT" >&2
+else
+	# Report on good results, and save any compilation output to log.
+	echo "ok: unsafe ${FUNC}() usage correctly detected with '$WANT' in $IN" >"$OUT"
+fi
+cat "$TMP" >>"$OUT"
diff --git a/lib/test_fortify/write_overflow-memcpy.c b/lib/test_fortify/write_overflow-memcpy.c
new file mode 100644
index 000000000..3b3984e42
--- /dev/null
+++ b/lib/test_fortify/write_overflow-memcpy.c
@@ -0,0 +1,5 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#define TEST	\
+	memcpy(instance.buf, large_src, sizeof(large_src))
+
+#include "test_fortify.h"
diff --git a/lib/test_fortify/write_overflow-memmove.c b/lib/test_fortify/write_overflow-memmove.c
new file mode 100644
index 000000000..640437c3b
--- /dev/null
+++ b/lib/test_fortify/write_overflow-memmove.c
@@ -0,0 +1,5 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#define TEST	\
+	memmove(instance.buf, large_src, sizeof(large_src))
+
+#include "test_fortify.h"
diff --git a/lib/test_fortify/write_overflow-memset.c b/lib/test_fortify/write_overflow-memset.c
new file mode 100644
index 000000000..36e34908c
--- /dev/null
+++ b/lib/test_fortify/write_overflow-memset.c
@@ -0,0 +1,5 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#define TEST	\
+	memset(instance.buf, 0x5A, sizeof(large_src))
+
+#include "test_fortify.h"
diff --git a/lib/test_fortify/write_overflow-strcpy-lit.c b/lib/test_fortify/write_overflow-strcpy-lit.c
new file mode 100644
index 000000000..51effb3e5
--- /dev/null
+++ b/lib/test_fortify/write_overflow-strcpy-lit.c
@@ -0,0 +1,5 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#define TEST	\
+	strcpy(small, LITERAL_LARGE)
+
+#include "test_fortify.h"
diff --git a/lib/test_fortify/write_overflow-strcpy.c b/lib/test_fortify/write_overflow-strcpy.c
new file mode 100644
index 000000000..84f1c56a6
--- /dev/null
+++ b/lib/test_fortify/write_overflow-strcpy.c
@@ -0,0 +1,5 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#define TEST	\
+	strcpy(small, large_src)
+
+#include "test_fortify.h"
diff --git a/lib/test_fortify/write_overflow-strscpy.c b/lib/test_fortify/write_overflow-strscpy.c
new file mode 100644
index 000000000..38feddf37
--- /dev/null
+++ b/lib/test_fortify/write_overflow-strscpy.c
@@ -0,0 +1,5 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#define TEST	\
+	strscpy(instance.buf, large_src, sizeof(instance.buf) + 1)
+
+#include "test_fortify.h"
diff --git a/lib/test_fortify/write_overflow_field-memcpy.c b/lib/test_fortify/write_overflow_field-memcpy.c
new file mode 100644
index 000000000..28cc81058
--- /dev/null
+++ b/lib/test_fortify/write_overflow_field-memcpy.c
@@ -0,0 +1,5 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#define TEST	\
+	memcpy(instance.buf, large, sizeof(instance.buf) + 1)
+
+#include "test_fortify.h"
diff --git a/lib/test_fortify/write_overflow_field-memmove.c b/lib/test_fortify/write_overflow_field-memmove.c
new file mode 100644
index 000000000..377fcf9bb
--- /dev/null
+++ b/lib/test_fortify/write_overflow_field-memmove.c
@@ -0,0 +1,5 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#define TEST	\
+	memmove(instance.buf, large, sizeof(instance.buf) + 1)
+
+#include "test_fortify.h"
diff --git a/lib/test_fortify/write_overflow_field-memset.c b/lib/test_fortify/write_overflow_field-memset.c
new file mode 100644
index 000000000..2331da269
--- /dev/null
+++ b/lib/test_fortify/write_overflow_field-memset.c
@@ -0,0 +1,5 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#define TEST	\
+	memset(instance.buf, 0x42, sizeof(instance.buf) + 1)
+
+#include "test_fortify.h"