On Thu, Apr 12, 2018 at 02:01:05PM +1000, David Gibson wrote: > On Tue, Apr 10, 2018 at 06:36:06PM -0400, Tom Rini wrote: > > On Tue, Apr 10, 2018 at 10:42:45AM -0400, Simon Glass wrote: > > > +U-Boot, Tom, Masahiro > > > > > > Hi David, > > > > > > On 10 April 2018 at 01:22, David Gibson <david@xxxxxxxxxxxxxxxxxxxxx> wrote: > > > > On Wed, Apr 04, 2018 at 01:21:10AM +0800, Simon Glass wrote: > > > >> Hi David, > > > >> > > > >> On 3 April 2018 at 23:02, David Gibson <david@xxxxxxxxxxxxxxxxxxxxx> wrote: > > > >> > > > > >> > On Fri, Mar 30, 2018 at 04:42:21PM +0800, Simon Glass wrote: > > > >> > > Hi David, > > > >> > > > > > >> > > On 26 March 2018 at 07:25, David Gibson <david@xxxxxxxxxxxxxxxxxxxxx> wrote: > > > >> > > > fdt_string() is used to retrieve strings from a DT blob's strings section. > > > >> > > > It's rarely used directly, but is widely used internally. > > > >> > > > > > > >> > > > However, it doesn't do any bounds checking, which means in the case of a > > > >> > > > corrupted blob it could access bad memory, which libfdt is supposed to > > > >> > > > avoid. > > > >> > > > > > > >> > > > This write a safe alternative to fdt_string, fdt_get_string(). It checks > > > >> > > > both that the given offset is within the string section and that the string > > > >> > > > it points to is properly \0 terminated within the section. It also returns > > > >> > > > the string's length as a convenience (since it needs to determine to do the > > > >> > > > checks anyway). > > > >> > > > > > > >> > > > fdt_string() is rewritten in terms of fdt_get_string() for compatibility. > > > >> > > > > > > >> > > > Most of the diff here is actually testing infrastructure. > > > >> > > > > > > >> > > > Signed-off-by: David Gibson <david@xxxxxxxxxxxxxxxxxxxxx> > > > >> > > > --- > > > >> > > > libfdt/fdt_ro.c | 61 +++++++++++++++++++++++++++++++++++-- > > > >> > > > libfdt/libfdt.h | 18 ++++++++++- > > > >> > > > libfdt/version.lds | 2 +- > > > >> > > > tests/.gitignore | 1 + > > > >> > > > tests/Makefile.tests | 2 +- > > > >> > > > tests/run_tests.sh | 1 + > > > >> > > > tests/testdata.h | 1 + > > > >> > > > tests/testutils.c | 11 +++++-- > > > >> > > > tests/trees.S | 26 ++++++++++++++++ > > > >> > > > tests/truncated_string.c | 79 ++++++++++++++++++++++++++++++++++++++++++++++++ > > > >> > > > 10 files changed, 193 insertions(+), 9 deletions(-) > > > >> > > > create mode 100644 tests/truncated_string.c > > > >> > > > > > >> > > Similar code-size quesiton here. It looks like a lot of checking code. > > > >> > > Can we have an option to remove it? > > > >> > > > > >> > Again, I'm disinclined without a concrete example of a problem. Fwiw > > > >> > the code size change is +276 bytes on my setup. > > > >> > > > >> That might not sound like a lot, but the overhead of DT in U-Boot is > > > >> about 3KB, so this adds nearly 10%. > > > > > > > > Hm. And how much is it compared to the whole U-Boot blob? > > > > > > > >> The specific problem is that when U-Boot SPL gets too big boards don't > > > >> boot. Because we take the upstream libfdt this will affect U-Boot. > > > >> > > > >> Do you have any thoughts on how we could avoid this size increase? > > > > > > > > So, again, I'm very disinclined to prioritize size over memory safety > > > > without a *concrete* example. i.e. "We hit this specific problem with > > > > size on this specific board that we were really using" rather than > > > > just "it might be a problem". > > > > I'm either failing in my Google-fu or is there not an easy way to grab > > the patches from patchwork/similar? But, if you shoot me the series > > off-list, I can tell you how much U-Boot targets grow here (we can use > > the same script as the kernel to re-sync sources back in, so I can give > > you a before/after). But as Simon notes, we have a number of platforms > > that need to use (parts of) libfdt and stick to ~30KiB or less in total, > > sometimes including some memory for stack/etc and we've long been using > > -ffunction-sections/etc (the latest round of trying to use LTO has me > > thinking maybe we can see if that's a valid option finally, but that's > > an aside). Thanks! > > We don't have a patchwork for these lists AFAIK, but you can get my > draft branch from: > > https://github.com/dgibson/dtc/tree/safety OK, thanks. So, I used scripts/dtc/update-dtc-source.sh to re-sync us first with current master, and then with the safety branch, and boy-howdy, are there a lot of warning changes and additions :) For the record, in U-Boot you can use the buildman tool (./tools/buildman/buildman) to build a series for a set of targets and get size change for each commit. I did: ./tools/buildman/buildman -o /tmp/libfdt-test -b master -SCdvel \ 'arc|arm|sandbox|x86|aarch64|powerpc|avr32|m68k|nios2|sh4|mips|xtensa|riscv' ./tools/buildman/buildman -o /tmp/libfdt-test -b master -Ssdel \ 'arc|arm|sandbox|x86|aarch64|powerpc|avr32|m68k|nios2|sh4|mips|xtensa|riscv' And the full results are at: https://gist.githubusercontent.com/trini/0f5f4c368de6c3f58d88cd55359e1468/raw/5f3a96de5c9ec3c7724ec182f9c513f255084a89/libfdt-size-change.txt Commit #1 that it built is the baseline results, commit #2 is current dtc master and commit #3 is with the safety branch. The good news is that nothing here is fatal (for targets that avail themselves of the CONFIG knobs to fail if binary size exceeds a certain target). Picking the BSC9132QDS_NOR_DDRCLK100_SECURE target and going for more detail on the growth we have: https://gist.github.com/trini/2c2ef7e839889279ac22fabf05360e4c#file-bsc9132qds_nor_ddrclk100_secure-txt-L7 That particular paste also shows that gcc-6.3 does a better job than gcc-5.4 (growth is 400 with 5.4 and 384 with gcc-6.3). Building for km_kirkwood_pci shows similar (but larger growth) results and are at https://gist.github.com/182af8446274dbda76553cbf924e2358 In sum, this isn't a deal-breaker yet, but is a real concern moving forward (and I will follow up to your other reply too). -- Tom
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