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Gianluca Borello a60dd35d2e bpf: change bpf_perf_event_output arg5 type to ARG_CONST_SIZE_OR_ZERO Commit `9fd29c08e5` ("bpf: improve verifier ARG_CONST_SIZE_OR_ZERO semantics") relaxed the treatment of ARG_CONST_SIZE_OR_ZERO due to the way the compiler generates optimized BPF code when checking boundaries of an argument from C code. A typical example of this optimized code can be generated using the bpf_perf_event_output helper when operating on variable memory: /* len is a generic scalar / if (len > 0 && len <= 0x7fff) bpf_perf_event_output(ctx, &perf_map, 0, buf, len); 110: (79) r5 = (u64 *)(r10 -40) 111: (bf) r1 = r5 112: (07) r1 += -1 113: (25) if r1 > 0x7ffe goto pc+6 114: (bf) r1 = r6 115: (18) r2 = 0xffff94e5f166c200 117: (b7) r3 = 0 118: (bf) r4 = r7 119: (85) call bpf_perf_event_output#25 R5 min value is negative, either use unsigned or 'var &= const' With this code, the verifier loses track of the variable. Replacing arg5 with ARG_CONST_SIZE_OR_ZERO is thus desirable since it avoids this quite common case which leads to usability issues, and the compiler generates code that the verifier can more easily test: if (len <= 0x7fff) bpf_perf_event_output(ctx, &perf_map, 0, buf, len); or bpf_perf_event_output(ctx, &perf_map, 0, buf, len & 0x7fff); No changes to the bpf_perf_event_output helper are necessary since it can handle a case where size is 0, and an empty frame is pushed. Reported-by: Arnaldo Carvalho de Melo <acme@redhat.com> Signed-off-by: Gianluca Borello <g.borello@gmail.com> Acked-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>		2017-11-22 21:40:54 +01:00
Documentation	…
arch	Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/sparc	2017-11-17 20:21:44 -08:00
block	…
certs	…
crypto	…
drivers	bpf: offload: move offload device validation out to the drivers	2017-11-21 00:37:35 +01:00
firmware	…
fs	…
include	bpf: introduce ARG_PTR_TO_MEM_OR_NULL	2017-11-22 21:40:54 +01:00
init	…
ipc	…
kernel	bpf: change bpf_perf_event_output arg5 type to ARG_CONST_SIZE_OR_ZERO	2017-11-22 21:40:54 +01:00
lib	…
mm	…
net	bpf: introduce ARG_PTR_TO_MEM_OR_NULL	2017-11-22 21:40:54 +01:00
samples	…
scripts	…
security	…
sound	…
tools	bpf: introduce ARG_PTR_TO_MEM_OR_NULL	2017-11-22 21:40:54 +01:00
usr	…
virt	…
.cocciconfig	…
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Kconfig	…
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Makefile	…
README	…

README

Linux kernel
============

This file was moved to Documentation/admin-guide/README.rst

Please notice that there are several guides for kernel developers and users.
These guides can be rendered in a number of formats, like HTML and PDF.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.