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75a1a607bb
Add two new probe_kernel_read_strict() and strncpy_from_unsafe_strict()
helpers which by default alias to the __probe_kernel_read() and the
__strncpy_from_unsafe(), respectively, but can be overridden by archs
which have non-overlapping address ranges for kernel space and user
space in order to bail out with -EFAULT when attempting to probe user
memory including non-canonical user access addresses [0]:
4-level page tables:
user-space mem: 0x0000000000000000 - 0x00007fffffffffff
non-canonical: 0x0000800000000000 - 0xffff7fffffffffff
5-level page tables:
user-space mem: 0x0000000000000000 - 0x00ffffffffffffff
non-canonical: 0x0100000000000000 - 0xfeffffffffffffff
The idea is that these helpers are complementary to the probe_user_read()
and strncpy_from_unsafe_user() which probe user-only memory. Both added
helpers here do the same, but for kernel-only addresses.
Both set of helpers are going to be used for BPF tracing. They also
explicitly avoid throwing the splat for non-canonical user addresses from
00c42373d3 ("x86-64: add warning for non-canonical user access address
dereferences").
For compat, the current probe_kernel_read() and strncpy_from_unsafe() are
left as-is.
[0] Documentation/x86/x86_64/mm.txt
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: x86@kernel.org
Link: https://lore.kernel.org/bpf/eefeefd769aa5a013531f491a71f0936779e916b.1572649915.git.daniel@iogearbox.net
43 lines
1.1 KiB
C
43 lines
1.1 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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#include <linux/uaccess.h>
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#include <linux/kernel.h>
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#ifdef CONFIG_X86_64
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static __always_inline u64 canonical_address(u64 vaddr, u8 vaddr_bits)
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{
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return ((s64)vaddr << (64 - vaddr_bits)) >> (64 - vaddr_bits);
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}
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static __always_inline bool invalid_probe_range(u64 vaddr)
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{
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/*
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* Range covering the highest possible canonical userspace address
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* as well as non-canonical address range. For the canonical range
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* we also need to include the userspace guard page.
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*/
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return vaddr < TASK_SIZE_MAX + PAGE_SIZE ||
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canonical_address(vaddr, boot_cpu_data.x86_virt_bits) != vaddr;
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}
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#else
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static __always_inline bool invalid_probe_range(u64 vaddr)
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{
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return vaddr < TASK_SIZE_MAX;
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}
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#endif
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long probe_kernel_read_strict(void *dst, const void *src, size_t size)
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{
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if (unlikely(invalid_probe_range((unsigned long)src)))
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return -EFAULT;
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return __probe_kernel_read(dst, src, size);
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}
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long strncpy_from_unsafe_strict(char *dst, const void *unsafe_addr, long count)
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{
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if (unlikely(invalid_probe_range((unsigned long)unsafe_addr)))
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return -EFAULT;
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return __strncpy_from_unsafe(dst, unsafe_addr, count);
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}
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