Commit 0ebeea8c authored by Daniel Borkmann's avatar Daniel Borkmann Committed by Alexei Starovoitov
Browse files

bpf: Restrict bpf_probe_read{, str}() only to archs where they work 



Given the legacy bpf_probe_read{,str}() BPF helpers are broken on archs
with overlapping address ranges, we should really take the next step to
disable them from BPF use there.

To generally fix the situation, we've recently added new helper variants
bpf_probe_read_{user,kernel}() and bpf_probe_read_{user,kernel}_str().
For details on them, see 6ae08ae3 ("bpf: Add probe_read_{user, kernel}
and probe_read_{user,kernel}_str helpers").

Given bpf_probe_read{,str}() have been around for ~5 years by now, there
are plenty of users at least on x86 still relying on them today, so we
cannot remove them entirely w/o breaking the BPF tracing ecosystem.

However, their use should be restricted to archs with non-overlapping
address ranges where they are working in their current form. Therefore,
move this behind a CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE and
have x86, arm64, arm select it (other archs supporting it can follow-up
on it as well).

For the remaining archs, they can workaround easily by relying on the
feature probe from bpftool which spills out defines that can be used out
of BPF C code to implement the drop-in replacement for old/new kernels
via: bpftool feature probe macro

Suggested-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Reviewed-by: default avatarMasami Hiramatsu <mhiramat@kernel.org>
Acked-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Cc: Brendan Gregg <brendan.d.gregg@gmail.com>
Cc: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/bpf/20200515101118.6508-2-daniel@iogearbox.net
parent 6d74f64b

arch/arm/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -12,6 +12,7 @@ config ARM 
	select ARCH_HAS_KEEPINITRD

	select ARCH_HAS_KCOV

	select ARCH_HAS_MEMBARRIER_SYNC_CORE

	select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE

	select ARCH_HAS_PTE_SPECIAL if ARM_LPAE

	select ARCH_HAS_PHYS_TO_DMA

	select ARCH_HAS_SETUP_DMA_OPS

arch/arm64/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -20,6 +20,7 @@ config ARM64 
	select ARCH_HAS_KCOV

	select ARCH_HAS_KEEPINITRD

	select ARCH_HAS_MEMBARRIER_SYNC_CORE

	select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE

	select ARCH_HAS_PTE_DEVMAP

	select ARCH_HAS_PTE_SPECIAL

	select ARCH_HAS_SETUP_DMA_OPS

arch/x86/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -68,6 +68,7 @@ config X86 
	select ARCH_HAS_KCOV			if X86_64

	select ARCH_HAS_MEM_ENCRYPT

	select ARCH_HAS_MEMBARRIER_SYNC_CORE

	select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE

	select ARCH_HAS_PMEM_API		if X86_64

	select ARCH_HAS_PTE_DEVMAP		if X86_64

	select ARCH_HAS_PTE_SPECIAL

init/Kconfig

+3 −0
Original line number Diff line number Diff line
@@ -2279,6 +2279,9 @@ config ASN1 


source "kernel/Kconfig.locks"



config ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE

	bool



config ARCH_HAS_SYNC_CORE_BEFORE_USERMODE

	bool

kernel/trace/bpf_trace.c

+4 −2
Original line number Diff line number Diff line
@@ -825,14 +825,16 @@ bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog) 
		return &bpf_probe_read_user_proto;

	case BPF_FUNC_probe_read_kernel:

		return &bpf_probe_read_kernel_proto;

	case BPF_FUNC_probe_read:

		return &bpf_probe_read_compat_proto;

	case BPF_FUNC_probe_read_user_str:

		return &bpf_probe_read_user_str_proto;

	case BPF_FUNC_probe_read_kernel_str:

		return &bpf_probe_read_kernel_str_proto;

#ifdef CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE

	case BPF_FUNC_probe_read:

		return &bpf_probe_read_compat_proto;

	case BPF_FUNC_probe_read_str:

		return &bpf_probe_read_compat_str_proto;

#endif

#ifdef CONFIG_CGROUPS

	case BPF_FUNC_get_current_cgroup_id:

		return &bpf_get_current_cgroup_id_proto;

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