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 6ae08ae3dea2 ("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: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Acked-by: Linus 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

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 66a04f6..c77c93c 100644 (file)
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -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

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 40fb05d..5d513f4 100644 (file)
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -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

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 1197b55..2d3f963 100644 (file)
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -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

diff --git a/init/Kconfig b/init/Kconfig
index 9e22ee8..6fd13a0 100644 (file)
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -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
 

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index ca17967..b83bdaa 100644 (file)
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -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;