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bpf: rework the compat kernel probe handling
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Instead of using the dangerous probe_kernel_read and strncpy_from_unsafe
helpers, rework the compat probes to check if an address is a kernel or
userspace one, and then use the low-level kernel or user probe helper
shared by the proper kernel and user probe helpers.  This slightly
changes behavior as the compat probe on a user address doesn't check
the lockdown flags, just as the pure user probes do.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20200521152301.2587579-14-hch@lst.de
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Christoph Hellwig authored and Linus Torvalds committed Jun 9, 2020
1 parent 19c8d8a commit 8d92db5
Showing 1 changed file with 67 additions and 42 deletions.
109 changes: 67 additions & 42 deletions kernel/trace/bpf_trace.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -136,17 +136,23 @@ static const struct bpf_func_proto bpf_override_return_proto = {
};
#endif

BPF_CALL_3(bpf_probe_read_user, void *, dst, u32, size,
const void __user *, unsafe_ptr)
static __always_inline int
bpf_probe_read_user_common(void *dst, u32 size, const void __user *unsafe_ptr)
{
int ret = probe_user_read(dst, unsafe_ptr, size);
int ret;

ret = probe_user_read(dst, unsafe_ptr, size);
if (unlikely(ret < 0))
memset(dst, 0, size);

return ret;
}

BPF_CALL_3(bpf_probe_read_user, void *, dst, u32, size,
const void __user *, unsafe_ptr)
{
return bpf_probe_read_user_common(dst, size, unsafe_ptr);
}

const struct bpf_func_proto bpf_probe_read_user_proto = {
.func = bpf_probe_read_user,
.gpl_only = true,
Expand All @@ -156,17 +162,24 @@ const struct bpf_func_proto bpf_probe_read_user_proto = {
.arg3_type = ARG_ANYTHING,
};

BPF_CALL_3(bpf_probe_read_user_str, void *, dst, u32, size,
const void __user *, unsafe_ptr)
static __always_inline int
bpf_probe_read_user_str_common(void *dst, u32 size,
const void __user *unsafe_ptr)
{
int ret = strncpy_from_user_nofault(dst, unsafe_ptr, size);
int ret;

ret = strncpy_from_user_nofault(dst, unsafe_ptr, size);
if (unlikely(ret < 0))
memset(dst, 0, size);

return ret;
}

BPF_CALL_3(bpf_probe_read_user_str, void *, dst, u32, size,
const void __user *, unsafe_ptr)
{
return bpf_probe_read_user_str_common(dst, size, unsafe_ptr);
}

const struct bpf_func_proto bpf_probe_read_user_str_proto = {
.func = bpf_probe_read_user_str,
.gpl_only = true,
Expand All @@ -177,25 +190,25 @@ const struct bpf_func_proto bpf_probe_read_user_str_proto = {
};

static __always_inline int
bpf_probe_read_kernel_common(void *dst, u32 size, const void *unsafe_ptr,
const bool compat)
bpf_probe_read_kernel_common(void *dst, u32 size, const void *unsafe_ptr)
{
int ret = security_locked_down(LOCKDOWN_BPF_READ);

if (unlikely(ret < 0))
goto out;
ret = compat ? probe_kernel_read(dst, unsafe_ptr, size) :
probe_kernel_read_strict(dst, unsafe_ptr, size);
goto fail;
ret = probe_kernel_read_strict(dst, unsafe_ptr, size);
if (unlikely(ret < 0))
out:
memset(dst, 0, size);
goto fail;
return ret;
fail:
memset(dst, 0, size);
return ret;
}

BPF_CALL_3(bpf_probe_read_kernel, void *, dst, u32, size,
const void *, unsafe_ptr)
{
return bpf_probe_read_kernel_common(dst, size, unsafe_ptr, false);
return bpf_probe_read_kernel_common(dst, size, unsafe_ptr);
}

const struct bpf_func_proto bpf_probe_read_kernel_proto = {
Expand All @@ -207,50 +220,37 @@ const struct bpf_func_proto bpf_probe_read_kernel_proto = {
.arg3_type = ARG_ANYTHING,
};

BPF_CALL_3(bpf_probe_read_compat, void *, dst, u32, size,
const void *, unsafe_ptr)
{
return bpf_probe_read_kernel_common(dst, size, unsafe_ptr, true);
}

static const struct bpf_func_proto bpf_probe_read_compat_proto = {
.func = bpf_probe_read_compat,
.gpl_only = true,
.ret_type = RET_INTEGER,
.arg1_type = ARG_PTR_TO_UNINIT_MEM,
.arg2_type = ARG_CONST_SIZE_OR_ZERO,
.arg3_type = ARG_ANYTHING,
};

static __always_inline int
bpf_probe_read_kernel_str_common(void *dst, u32 size, const void *unsafe_ptr,
const bool compat)
bpf_probe_read_kernel_str_common(void *dst, u32 size, const void *unsafe_ptr)
{
int ret = security_locked_down(LOCKDOWN_BPF_READ);

if (unlikely(ret < 0))
goto out;
goto fail;

/*
* The strncpy_from_unsafe_*() call will likely not fill the entire
* buffer, but that's okay in this circumstance as we're probing
* The strncpy_from_kernel_nofault() call will likely not fill the
* entire buffer, but that's okay in this circumstance as we're probing
* arbitrary memory anyway similar to bpf_probe_read_*() and might
* as well probe the stack. Thus, memory is explicitly cleared
* only in error case, so that improper users ignoring return
* code altogether don't copy garbage; otherwise length of string
* is returned that can be used for bpf_perf_event_output() et al.
*/
ret = compat ? strncpy_from_unsafe(dst, unsafe_ptr, size) :
strncpy_from_kernel_nofault(dst, unsafe_ptr, size);
ret = strncpy_from_kernel_nofault(dst, unsafe_ptr, size);
if (unlikely(ret < 0))
out:
memset(dst, 0, size);
goto fail;

return 0;
fail:
memset(dst, 0, size);
return ret;
}

BPF_CALL_3(bpf_probe_read_kernel_str, void *, dst, u32, size,
const void *, unsafe_ptr)
{
return bpf_probe_read_kernel_str_common(dst, size, unsafe_ptr, false);
return bpf_probe_read_kernel_str_common(dst, size, unsafe_ptr);
}

const struct bpf_func_proto bpf_probe_read_kernel_str_proto = {
Expand All @@ -262,10 +262,34 @@ const struct bpf_func_proto bpf_probe_read_kernel_str_proto = {
.arg3_type = ARG_ANYTHING,
};

#ifdef CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
BPF_CALL_3(bpf_probe_read_compat, void *, dst, u32, size,
const void *, unsafe_ptr)
{
if ((unsigned long)unsafe_ptr < TASK_SIZE) {
return bpf_probe_read_user_common(dst, size,
(__force void __user *)unsafe_ptr);
}
return bpf_probe_read_kernel_common(dst, size, unsafe_ptr);
}

static const struct bpf_func_proto bpf_probe_read_compat_proto = {
.func = bpf_probe_read_compat,
.gpl_only = true,
.ret_type = RET_INTEGER,
.arg1_type = ARG_PTR_TO_UNINIT_MEM,
.arg2_type = ARG_CONST_SIZE_OR_ZERO,
.arg3_type = ARG_ANYTHING,
};

BPF_CALL_3(bpf_probe_read_compat_str, void *, dst, u32, size,
const void *, unsafe_ptr)
{
return bpf_probe_read_kernel_str_common(dst, size, unsafe_ptr, true);
if ((unsigned long)unsafe_ptr < TASK_SIZE) {
return bpf_probe_read_user_str_common(dst, size,
(__force void __user *)unsafe_ptr);
}
return bpf_probe_read_kernel_str_common(dst, size, unsafe_ptr);
}

static const struct bpf_func_proto bpf_probe_read_compat_str_proto = {
Expand All @@ -276,6 +300,7 @@ static const struct bpf_func_proto bpf_probe_read_compat_str_proto = {
.arg2_type = ARG_CONST_SIZE_OR_ZERO,
.arg3_type = ARG_ANYTHING,
};
#endif /* CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE */

BPF_CALL_3(bpf_probe_write_user, void __user *, unsafe_ptr, const void *, src,
u32, size)
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