On Sat, Aug 10, 2024 at 2:49 AM Kui-Feng Lee <sinquersw@xxxxxxxxx> wrote:
>
>
>
> On 8/9/24 14:23, Jordan Rome wrote:
> > 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.
> >
> > Signed-off-by: Jordan Rome <linux@xxxxxxxxxxxxxx>
> > ---
> > kernel/bpf/helpers.c | 26 +++++++++++++++++++
> > .../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 | 24 ++++++++++++++---
> > 5 files changed, 61 insertions(+), 7 deletions(-)
> >
> > diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> > index d02ae323996b..455cac7b2631 100644
> > --- a/kernel/bpf/helpers.c
> > +++ b/kernel/bpf/helpers.c
> > @@ -2939,6 +2939,31 @@ __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.
> > + *
> > + * 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.
> > + */
> > +__bpf_kfunc int bpf_copy_from_user_str(void *dst, u32 dst__szk, const void __user *unsafe_ptr__ign)
> > +{
> > + int ret;
> > +
> > + if (unlikely(!dst__szk))
> > + return 0;
> > +
> > + ret = strncpy_from_user(dst, unsafe_ptr__ign, dst__szk);
>
> Does this function promise dst is null terminated if ret >= 0?
> It seems not to have null at the end if the source string is longer than
> dst_szk.
>
>
Good catch. I need to copy the same logic that exists in
`strncpy_from_user_nofault` which sets the last byte to '\0'.
> > + if (unlikely(ret < 0))
> > + memset(dst, 0, dst__szk);
> > +
> > + return ret;
> > +}
> > +
> > __bpf_kfunc_end_defs();
> >
> > BTF_KFUNCS_START(generic_btf_ids)
> > @@ -3024,6 +3049,7 @@ 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/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..27de1e907754 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 *) __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);
> >
> > 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..a90fa0bf103b 100644
> > --- a/tools/testing/selftests/bpf/progs/test_attach_probe.c
> > +++ b/tools/testing/selftests/bpf/progs/test_attach_probe.c
> > @@ -14,11 +14,15 @@ 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 *) __weak __ksym;
> > +
> > SEC("ksyscall/nanosleep")
> > int BPF_KSYSCALL(handle_kprobe_auto, struct __kernel_timespec *req, struct __kernel_timespec *rem)
> > {
> > @@ -87,11 +91,23 @@ 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[10];
> > +
> > + ret = bpf_copy_from_user_str(data, sizeof(data), user_ptr);
> > +
> > + return bpf_strncmp(data, sizeof(data), "test_data") == 0 && ret == 9;
> > +}
> > +
> > 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 +118,7 @@ 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 +126,16 @@ 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;
> > }
> >
> > --
> > 2.44.1
> >
> >
