mirror of
https://kernel.googlesource.com/pub/scm/linux/kernel/git/torvalds/linux
synced 2025-09-17 18:16:22 +10:00
c40160f299
While the latent entropy plugin mostly doesn't derive entropy from
get_random_const() for measuring the call graph, when __latent_entropy is
applied to a constant, then it's initialized statically to output from
get_random_const(). In that case, this data is derived from a 64-bit
seed, which means a buffer of 512 bits doesn't really have that amount
of compile-time entropy.
This patch fixes that shortcoming by just buffering chunks of
/dev/urandom output and doling it out as requested.
At the same time, it's important that we don't break the use of
-frandom-seed, for people who want the runtime benefits of the latent
entropy plugin, while still having compile-time determinism. In that
case, we detect whether gcc's set_random_seed() has been called by
making a call to get_random_seed(noinit=true) in the plugin init
function, which is called after set_random_seed() is called but before
anything that calls get_random_seed(noinit=false), and seeing if it's
zero or not. If it's not zero, we're in deterministic mode, and so we
just generate numbers with a basic xorshift prng.
Note that we don't detect if -frandom-seed is being used using the
documented local_tick variable, because it's assigned via:
local_tick = (unsigned) tv.tv_sec * 1000 + tv.tv_usec / 1000;
which may well overflow and become -1 on its own, and so isn't
reliable: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105171
[kees: The 256 byte rnd_buf size was chosen based on average (250),
median (64), and std deviation (575) bytes of used entropy for a
defconfig x86_64 build]
Fixes:
|
||
|---|---|---|
| .. | ||
| atomic | ||
| basic | ||
| clang-tools | ||
| coccinelle | ||
| dtc | ||
| dummy-tools | ||
| gcc-plugins | ||
| gdb | ||
| genksyms | ||
| kconfig | ||
| ksymoops | ||
| mod | ||
| package | ||
| selinux | ||
| tracing | ||
| .gitignore | ||
| adjust_autoksyms.sh | ||
| as-version.sh | ||
| asn1_compiler.c | ||
| bin2c.c | ||
| bloat-o-meter | ||
| bootgraph.pl | ||
| bpf_doc.py | ||
| cc-can-link.sh | ||
| cc-version.sh | ||
| check_extable.sh | ||
| check-sysctl-docs | ||
| checkdeclares.pl | ||
| checkincludes.pl | ||
| checkkconfigsymbols.py | ||
| checkpatch.pl | ||
| checkstack.pl | ||
| checksyscalls.sh | ||
| checkversion.pl | ||
| cleanfile | ||
| cleanpatch | ||
| coccicheck | ||
| config | ||
| const_structs.checkpatch | ||
| decode_stacktrace.sh | ||
| decodecode | ||
| depmod.sh | ||
| dev-needs.sh | ||
| diffconfig | ||
| documentation-file-ref-check | ||
| export_report.pl | ||
| extract_xc3028.pl | ||
| extract-ikconfig | ||
| extract-module-sig.pl | ||
| extract-sys-certs.pl | ||
| extract-vmlinux | ||
| faddr2line | ||
| file-size.sh | ||
| find-unused-docs.sh | ||
| gcc-goto.sh | ||
| gcc-ld | ||
| gcc-x86_32-has-stack-protector.sh | ||
| gcc-x86_64-has-stack-protector.sh | ||
| gen_autoksyms.sh | ||
| gen_ksymdeps.sh | ||
| generate_initcall_order.pl | ||
| get_abi.pl | ||
| get_dvb_firmware | ||
| get_feat.pl | ||
| get_maintainer.pl | ||
| gfp-translate | ||
| headerdep.pl | ||
| headers_install.sh | ||
| insert-sys-cert.c | ||
| jobserver-exec | ||
| kallsyms.c | ||
| Kbuild.include | ||
| Kconfig.include | ||
| kernel-doc | ||
| ld-version.sh | ||
| leaking_addresses.pl | ||
| Lindent | ||
| link-vmlinux.sh | ||
| Makefile | ||
| Makefile.asm-generic | ||
| Makefile.build | ||
| Makefile.clang | ||
| Makefile.clean | ||
| Makefile.compiler | ||
| Makefile.debug | ||
| Makefile.dtbinst | ||
| Makefile.extrawarn | ||
| Makefile.gcc-plugins | ||
| Makefile.headersinst | ||
| Makefile.host | ||
| Makefile.kasan | ||
| Makefile.kcov | ||
| Makefile.kcsan | ||
| Makefile.lib | ||
| Makefile.modfinal | ||
| Makefile.modinst | ||
| Makefile.modpost | ||
| Makefile.package | ||
| Makefile.ubsan | ||
| Makefile.userprogs | ||
| makelst | ||
| markup_oops.pl | ||
| min-tool-version.sh | ||
| mkcompile_h | ||
| mksysmap | ||
| mkuboot.sh | ||
| module.lds.S | ||
| modules-check.sh | ||
| nsdeps | ||
| objdiff | ||
| pahole-flags.sh | ||
| parse-maintainers.pl | ||
| patch-kernel | ||
| profile2linkerlist.pl | ||
| prune-kernel | ||
| recordmcount.c | ||
| recordmcount.h | ||
| recordmcount.pl | ||
| remove-stale-files | ||
| setlocalversion | ||
| show_delta | ||
| sign-file.c | ||
| sorttable.c | ||
| sorttable.h | ||
| spdxcheck-test.sh | ||
| spdxcheck.py | ||
| spelling.txt | ||
| sphinx-pre-install | ||
| split-man.pl | ||
| stackdelta | ||
| stackusage | ||
| subarch.include | ||
| syscallhdr.sh | ||
| syscallnr.sh | ||
| syscalltbl.sh | ||
| tags.sh | ||
| test_fortify.sh | ||
| tools-support-relr.sh | ||
| unifdef.c | ||
| ver_linux | ||
| xen-hypercalls.sh | ||
| xz_wrap.sh | ||