[bpf-next v8 1/2] bpf: Add bpf_copy_from_user_str kfunc

[bpf-next v8 1/2] bpf: Add bpf_copy_from_user_str kfunc

[Jordan Rome]

This adds a kfunc wrapper around strncpy_from_user,
which can be called from sleepable BPF programs.

This matches the non-sleepable 'bpf_probe_read_user_str'
helper except it includes an additional 'flags'
param, which allows consumers to clear the entire
destination buffer on success or failure.

Signed-off-by: Jordan Rome <linux@jordanrome.com>
---
 include/uapi/linux/bpf.h       |  9 ++++++++
 kernel/bpf/helpers.c           | 42 ++++++++++++++++++++++++++++++++++
 tools/include/uapi/linux/bpf.h |  9 ++++++++
 3 files changed, 60 insertions(+)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index e05b39e39c3f..8556f65da4f8 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -7513,4 +7513,13 @@ struct bpf_iter_num {
 	__u64 __opaque[1];
 } __attribute__((aligned(8)));

+/*
+ * Flags to control bpf_copy_from_user_str() behaviour.
+ *     - BPF_F_PAD_ZEROS: Pad destination buffer with zeros. (See the respective
+ *       helper documentation for details.)
+ */
+enum {
+	BPF_F_PAD_ZEROS = (1ULL << 0),
+};
+
 #endif /* _UAPI__LINUX_BPF_H__ */
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index d02ae323996b..e5614a980d59 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -2939,6 +2939,47 @@ __bpf_kfunc void bpf_iter_bits_destroy(struct bpf_iter_bits *it)
 	bpf_mem_free(&bpf_global_ma, kit->bits);
 }

+/**
+ * bpf_copy_from_user_str() - Copy a string from an unsafe user address
+ * @dst:             Destination address, in kernel space.  This buffer must be at
+ *                   least @dst__szk bytes long.
+ * @dst__szk:        Maximum number of bytes to copy, including the trailing NUL.
+ * @unsafe_ptr__ign: Source address, in user space.
+ * @flags:           The only supported flag is BPF_F_PAD_ZEROS
+ *
+ * Copies a NUL-terminated string from userspace to BPF space. If user string is
+ * too long this will still ensure zero termination in the dst buffer unless
+ * buffer size is 0.
+ *
+ * If BPF_F_PAD_ZEROS flag is set, memset the tail of @dst to 0 on success and
+ * memset all of @dst on failure.
+ */
+__bpf_kfunc int bpf_copy_from_user_str(void *dst, u32 dst__szk, const void __user *unsafe_ptr__ign, u64 flags)
+{
+	int ret;
+
+	if (unlikely(flags & ~BPF_F_PAD_ZEROS))
+		return -EINVAL;
+
+	if (unlikely(!dst__szk))
+		return 0;
+
+	ret = strncpy_from_user(dst, unsafe_ptr__ign, dst__szk - 1);
+	if (ret < 0) {
+		if (flags & BPF_F_PAD_ZEROS)
+			memset((char *)dst, 0, dst__szk);
+
+		return ret;
+	}
+
+	if (flags & BPF_F_PAD_ZEROS)
+		memset((char *)dst + ret, 0, dst__szk - ret);
+	else
+		((char *)dst)[ret] = '\0';
+
+	return ret + 1;
+}
+
 __bpf_kfunc_end_defs();

 BTF_KFUNCS_START(generic_btf_ids)
@@ -3024,6 +3065,7 @@ BTF_ID_FLAGS(func, bpf_preempt_enable)
 BTF_ID_FLAGS(func, bpf_iter_bits_new, KF_ITER_NEW)
 BTF_ID_FLAGS(func, bpf_iter_bits_next, KF_ITER_NEXT | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_iter_bits_destroy, KF_ITER_DESTROY)
+BTF_ID_FLAGS(func, bpf_copy_from_user_str, KF_SLEEPABLE)
 BTF_KFUNCS_END(common_btf_ids)

 static const struct btf_kfunc_id_set common_kfunc_set = {
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index e05b39e39c3f..8556f65da4f8 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -7513,4 +7513,13 @@ struct bpf_iter_num {
 	__u64 __opaque[1];
 } __attribute__((aligned(8)));

+/*
+ * Flags to control bpf_copy_from_user_str() behaviour.
+ *     - BPF_F_PAD_ZEROS: Pad destination buffer with zeros. (See the respective
+ *       helper documentation for details.)
+ */
+enum {
+	BPF_F_PAD_ZEROS = (1ULL << 0),
+};
+
 #endif /* _UAPI__LINUX_BPF_H__ */
--
2.43.5

[bpf-next v8 2/2] bpf: Add tests for bpf_copy_from_user_str kfunc

[Jordan Rome]

This adds tests for both the happy path and
the error path.

Signed-off-by: Jordan Rome <linux@jordanrome.com>
---
 .../selftests/bpf/prog_tests/attach_probe.c   |  8 ++-
 .../selftests/bpf/prog_tests/read_vsyscall.c  |  1 +
 .../selftests/bpf/progs/read_vsyscall.c       |  9 ++-
 .../selftests/bpf/progs/test_attach_probe.c   | 57 ++++++++++++++++++-
 4 files changed, 68 insertions(+), 7 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/attach_probe.c b/tools/testing/selftests/bpf/prog_tests/attach_probe.c
index 7175af39134f..329c7862b52d 100644
--- a/tools/testing/selftests/bpf/prog_tests/attach_probe.c
+++ b/tools/testing/selftests/bpf/prog_tests/attach_probe.c
@@ -283,9 +283,11 @@ static void test_uprobe_sleepable(struct test_attach_probe *skel)
 	trigger_func3();

 	ASSERT_EQ(skel->bss->uprobe_byname3_sleepable_res, 9, "check_uprobe_byname3_sleepable_res");
-	ASSERT_EQ(skel->bss->uprobe_byname3_res, 10, "check_uprobe_byname3_res");
-	ASSERT_EQ(skel->bss->uretprobe_byname3_sleepable_res, 11, "check_uretprobe_byname3_sleepable_res");
-	ASSERT_EQ(skel->bss->uretprobe_byname3_res, 12, "check_uretprobe_byname3_res");
+	ASSERT_EQ(skel->bss->uprobe_byname3_str_sleepable_res, 10, "check_uprobe_byname3_str_sleepable_res");
+	ASSERT_EQ(skel->bss->uprobe_byname3_res, 11, "check_uprobe_byname3_res");
+	ASSERT_EQ(skel->bss->uretprobe_byname3_sleepable_res, 12, "check_uretprobe_byname3_sleepable_res");
+	ASSERT_EQ(skel->bss->uretprobe_byname3_str_sleepable_res, 13, "check_uretprobe_byname3_str_sleepable_res");
+	ASSERT_EQ(skel->bss->uretprobe_byname3_res, 14, "check_uretprobe_byname3_res");
 }

 void test_attach_probe(void)
diff --git a/tools/testing/selftests/bpf/prog_tests/read_vsyscall.c b/tools/testing/selftests/bpf/prog_tests/read_vsyscall.c
index 3405923fe4e6..c7b9ba8b1d06 100644
--- a/tools/testing/selftests/bpf/prog_tests/read_vsyscall.c
+++ b/tools/testing/selftests/bpf/prog_tests/read_vsyscall.c
@@ -23,6 +23,7 @@ struct read_ret_desc {
 	{ .name = "probe_read_user_str", .ret = -EFAULT },
 	{ .name = "copy_from_user", .ret = -EFAULT },
 	{ .name = "copy_from_user_task", .ret = -EFAULT },
+	{ .name = "copy_from_user_str", .ret = -EFAULT },
 };

 void test_read_vsyscall(void)
diff --git a/tools/testing/selftests/bpf/progs/read_vsyscall.c b/tools/testing/selftests/bpf/progs/read_vsyscall.c
index 986f96687ae1..39ebef430059 100644
--- a/tools/testing/selftests/bpf/progs/read_vsyscall.c
+++ b/tools/testing/selftests/bpf/progs/read_vsyscall.c
@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
 /* Copyright (C) 2024. Huawei Technologies Co., Ltd */
+#include "vmlinux.h"
 #include <linux/types.h>
 #include <bpf/bpf_helpers.h>

@@ -7,10 +8,15 @@

 int target_pid = 0;
 void *user_ptr = 0;
-int read_ret[8];
+int read_ret[9];

 char _license[] SEC("license") = "GPL";

+/*
+ * This is the only kfunc, the others are helpers
+ */
+int bpf_copy_from_user_str(void *dst, u32, const void *, u64) __weak __ksym;
+
 SEC("fentry/" SYS_PREFIX "sys_nanosleep")
 int do_probe_read(void *ctx)
 {
@@ -40,6 +46,7 @@ int do_copy_from_user(void *ctx)
 	read_ret[6] = bpf_copy_from_user(buf, sizeof(buf), user_ptr);
 	read_ret[7] = bpf_copy_from_user_task(buf, sizeof(buf), user_ptr,
 					      bpf_get_current_task_btf(), 0);
+	read_ret[8] = bpf_copy_from_user_str((char *)buf, sizeof(buf), user_ptr, 0);

 	return 0;
 }
diff --git a/tools/testing/selftests/bpf/progs/test_attach_probe.c b/tools/testing/selftests/bpf/progs/test_attach_probe.c
index 68466a6ad18c..4959eda92479 100644
--- a/tools/testing/selftests/bpf/progs/test_attach_probe.c
+++ b/tools/testing/selftests/bpf/progs/test_attach_probe.c
@@ -5,6 +5,7 @@
 #include <bpf/bpf_helpers.h>
 #include <bpf/bpf_tracing.h>
 #include <bpf/bpf_core_read.h>
+#include <errno.h>
 #include "bpf_misc.h"

 int kprobe2_res = 0;
@@ -14,11 +15,15 @@ int uretprobe_byname_res = 0;
 int uprobe_byname2_res = 0;
 int uretprobe_byname2_res = 0;
 int uprobe_byname3_sleepable_res = 0;
+int uprobe_byname3_str_sleepable_res = 0;
 int uprobe_byname3_res = 0;
 int uretprobe_byname3_sleepable_res = 0;
+int uretprobe_byname3_str_sleepable_res = 0;
 int uretprobe_byname3_res = 0;
 void *user_ptr = 0;

+int bpf_copy_from_user_str(void *dst, u32, const void *, u64) __weak __ksym;
+
 SEC("ksyscall/nanosleep")
 int BPF_KSYSCALL(handle_kprobe_auto, struct __kernel_timespec *req, struct __kernel_timespec *rem)
 {
@@ -87,11 +92,55 @@ static __always_inline bool verify_sleepable_user_copy(void)
 	return bpf_strncmp(data, sizeof(data), "test_data") == 0;
 }

+static __always_inline bool verify_sleepable_user_copy_str(void)
+{
+	int ret;
+	char data_long[20];
+	char data_long_pad[20];
+	char data_long_err[20];
+	char data_short[4];
+	char data_short_pad[4];
+
+	ret = bpf_copy_from_user_str(data_short, sizeof(data_short), user_ptr, 0);
+
+	if (bpf_strncmp(data_short, 4, "tes\0") != 0 || ret != 4)
+		return false;
+
+	ret = bpf_copy_from_user_str(data_short_pad, sizeof(data_short_pad), user_ptr, BPF_F_PAD_ZEROS);
+
+	if (bpf_strncmp(data_short, 4, "tes\0") != 0 || ret != 4)
+		return false;
+
+	ret = bpf_copy_from_user_str(data_long, sizeof(data_long), user_ptr, 0);
+
+	if (bpf_strncmp(data_long, 10, "test_data\0") != 0 || ret != 10)
+		return false;
+
+	ret = bpf_copy_from_user_str(data_long_pad, sizeof(data_long_pad), user_ptr, BPF_F_PAD_ZEROS);
+
+	if (bpf_strncmp(data_long_pad, 10, "test_data\0") != 0 || ret != 10 || data_long_pad[19] != '\0')
+		return false;
+
+	ret = bpf_copy_from_user_str(data_long_err, sizeof(data_long_err), (void *)data_long, BPF_F_PAD_ZEROS);
+
+	if (ret > 0 || data_long_err[19] != '\0')
+		return false;
+
+	ret = bpf_copy_from_user_str(data_long, sizeof(data_long), user_ptr, 2);
+
+	if (ret != -EINVAL)
+		return false;
+
+	return true;
+}
+
 SEC("uprobe.s//proc/self/exe:trigger_func3")
 int handle_uprobe_byname3_sleepable(struct pt_regs *ctx)
 {
 	if (verify_sleepable_user_copy())
 		uprobe_byname3_sleepable_res = 9;
+	if (verify_sleepable_user_copy_str())
+		uprobe_byname3_str_sleepable_res = 10;
 	return 0;
 }

@@ -102,7 +151,7 @@ int handle_uprobe_byname3_sleepable(struct pt_regs *ctx)
 SEC("uprobe//proc/self/exe:trigger_func3")
 int handle_uprobe_byname3(struct pt_regs *ctx)
 {
-	uprobe_byname3_res = 10;
+	uprobe_byname3_res = 11;
 	return 0;
 }

@@ -110,14 +159,16 @@ SEC("uretprobe.s//proc/self/exe:trigger_func3")
 int handle_uretprobe_byname3_sleepable(struct pt_regs *ctx)
 {
 	if (verify_sleepable_user_copy())
-		uretprobe_byname3_sleepable_res = 11;
+		uretprobe_byname3_sleepable_res = 12;
+	if (verify_sleepable_user_copy_str())
+		uretprobe_byname3_str_sleepable_res = 13;
 	return 0;
 }

 SEC("uretprobe//proc/self/exe:trigger_func3")
 int handle_uretprobe_byname3(struct pt_regs *ctx)
 {
-	uretprobe_byname3_res = 12;
+	uretprobe_byname3_res = 14;
 	return 0;
 }

--
2.43.5

Re: [bpf-next v8 1/2] bpf: Add bpf_copy_from_user_str kfunc

[Alexei Starovoitov]

On Thu, Aug 22, 2024 at 5:06 PM Jordan Rome <linux@jordanrome.com> wrote:
>
> +/**
> + * bpf_copy_from_user_str() - Copy a string from an unsafe user address
> + * @dst:             Destination address, in kernel space.  This buffer must be at
> + *                   least @dst__szk bytes long.
> + * @dst__szk:        Maximum number of bytes to copy, including the trailing NUL.
> + * @unsafe_ptr__ign: Source address, in user space.
> + * @flags:           The only supported flag is BPF_F_PAD_ZEROS
> + *
> + * Copies a NUL-terminated string from userspace to BPF space. If user string is
> + * too long this will still ensure zero termination in the dst buffer unless
> + * buffer size is 0.
> + *
> + * If BPF_F_PAD_ZEROS flag is set, memset the tail of @dst to 0 on success and
> + * memset all of @dst on failure.
> + */
> +__bpf_kfunc int bpf_copy_from_user_str(void *dst, u32 dst__szk, const void __user *unsafe_ptr__ign, u64 flags)

Did you miss my previous comment re __szk vs __sz ?

> +enum {
> +       BPF_F_PAD_ZEROS = (1ULL << 0),
> +};

Pls give enum a name, so it's easier for CORE logic to detect the
presence of this feature in the kernel.

Re: [bpf-next v8 1/2] bpf: Add bpf_copy_from_user_str kfunc

[Jordan Rome]

On Thu, Aug 22, 2024 at 8:15 PM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Thu, Aug 22, 2024 at 5:06 PM Jordan Rome <linux@jordanrome.com> wrote:
> >
> > +/**
> > + * bpf_copy_from_user_str() - Copy a string from an unsafe user address
> > + * @dst:             Destination address, in kernel space.  This buffer must be at
> > + *                   least @dst__szk bytes long.
> > + * @dst__szk:        Maximum number of bytes to copy, including the trailing NUL.
> > + * @unsafe_ptr__ign: Source address, in user space.
> > + * @flags:           The only supported flag is BPF_F_PAD_ZEROS
> > + *
> > + * Copies a NUL-terminated string from userspace to BPF space. If user string is
> > + * too long this will still ensure zero termination in the dst buffer unless
> > + * buffer size is 0.
> > + *
> > + * If BPF_F_PAD_ZEROS flag is set, memset the tail of @dst to 0 on success and
> > + * memset all of @dst on failure.
> > + */
> > +__bpf_kfunc int bpf_copy_from_user_str(void *dst, u32 dst__szk, const void __user *unsafe_ptr__ign, u64 flags)
>
> Did you miss my previous comment re __szk vs __sz ?
>

Ah, yes, I did miss it. Will fix.

> > +enum {
> > +       BPF_F_PAD_ZEROS = (1ULL << 0),
> > +};
>
> Pls give enum a name, so it's easier for CORE logic to detect the
> presence of this feature in the kernel.

How about 'bpf_copy_str_flags' ? As I imagine we will use this flag on
'bpf_copy_from_user_task_str', when I add that.

Re: [bpf-next v8 1/2] bpf: Add bpf_copy_from_user_str kfunc

[Alexei Starovoitov]

On Thu, Aug 22, 2024 at 5:22 PM Jordan Rome <linux@jordanrome.com> wrote:
>
> On Thu, Aug 22, 2024 at 8:15 PM Alexei Starovoitov
> <alexei.starovoitov@gmail.com> wrote:
> >
> > On Thu, Aug 22, 2024 at 5:06 PM Jordan Rome <linux@jordanrome.com> wrote:
> > >
> > > +/**
> > > + * bpf_copy_from_user_str() - Copy a string from an unsafe user address
> > > + * @dst:             Destination address, in kernel space.  This buffer must be at
> > > + *                   least @dst__szk bytes long.
> > > + * @dst__szk:        Maximum number of bytes to copy, including the trailing NUL.
> > > + * @unsafe_ptr__ign: Source address, in user space.
> > > + * @flags:           The only supported flag is BPF_F_PAD_ZEROS
> > > + *
> > > + * Copies a NUL-terminated string from userspace to BPF space. If user string is
> > > + * too long this will still ensure zero termination in the dst buffer unless
> > > + * buffer size is 0.
> > > + *
> > > + * If BPF_F_PAD_ZEROS flag is set, memset the tail of @dst to 0 on success and
> > > + * memset all of @dst on failure.
> > > + */
> > > +__bpf_kfunc int bpf_copy_from_user_str(void *dst, u32 dst__szk, const void __user *unsafe_ptr__ign, u64 flags)
> >
> > Did you miss my previous comment re __szk vs __sz ?
> >
>
> Ah, yes, I did miss it. Will fix.
>
> > > +enum {
> > > +       BPF_F_PAD_ZEROS = (1ULL << 0),
> > > +};
> >
> > Pls give enum a name, so it's easier for CORE logic to detect the
> > presence of this feature in the kernel.
>
> How about 'bpf_copy_str_flags' ? As I imagine we will use this flag on
> 'bpf_copy_from_user_task_str', when I add that.

Maybe 'enum bpf_kfunc_flags' ?
since BPF_F_PAD_ZEROS is supposed to be generic and apply to various kfuncs.

Re: [bpf-next v8 1/2] bpf: Add bpf_copy_from_user_str kfunc

[Jordan Rome]

On Thu, Aug 22, 2024 at 8:45 PM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Thu, Aug 22, 2024 at 5:22 PM Jordan Rome <linux@jordanrome.com> wrote:
> >
> > On Thu, Aug 22, 2024 at 8:15 PM Alexei Starovoitov
> > <alexei.starovoitov@gmail.com> wrote:
> > >
> > > On Thu, Aug 22, 2024 at 5:06 PM Jordan Rome <linux@jordanrome.com> wrote:
> > > >
> > > > +/**
> > > > + * bpf_copy_from_user_str() - Copy a string from an unsafe user address
> > > > + * @dst:             Destination address, in kernel space.  This buffer must be at
> > > > + *                   least @dst__szk bytes long.
> > > > + * @dst__szk:        Maximum number of bytes to copy, including the trailing NUL.
> > > > + * @unsafe_ptr__ign: Source address, in user space.
> > > > + * @flags:           The only supported flag is BPF_F_PAD_ZEROS
> > > > + *
> > > > + * Copies a NUL-terminated string from userspace to BPF space. If user string is
> > > > + * too long this will still ensure zero termination in the dst buffer unless
> > > > + * buffer size is 0.
> > > > + *
> > > > + * If BPF_F_PAD_ZEROS flag is set, memset the tail of @dst to 0 on success and
> > > > + * memset all of @dst on failure.
> > > > + */
> > > > +__bpf_kfunc int bpf_copy_from_user_str(void *dst, u32 dst__szk, const void __user *unsafe_ptr__ign, u64 flags)
> > >
> > > Did you miss my previous comment re __szk vs __sz ?
> > >
> >
> > Ah, yes, I did miss it. Will fix.
> >
> > > > +enum {
> > > > +       BPF_F_PAD_ZEROS = (1ULL << 0),
> > > > +};
> > >
> > > Pls give enum a name, so it's easier for CORE logic to detect the
> > > presence of this feature in the kernel.
> >
> > How about 'bpf_copy_str_flags' ? As I imagine we will use this flag on
> > 'bpf_copy_from_user_task_str', when I add that.
>
> Maybe 'enum bpf_kfunc_flags' ?
> since BPF_F_PAD_ZEROS is supposed to be generic and apply to various kfuncs.

Works for me.