forked from Minki/linux
eab09532d4
The ELF_ET_DYN_BASE position was originally intended to keep loaders
away from ET_EXEC binaries. (For example, running "/lib/ld-linux.so.2
/bin/cat" might cause the subsequent load of /bin/cat into where the
loader had been loaded.)
With the advent of PIE (ET_DYN binaries with an INTERP Program Header),
ELF_ET_DYN_BASE continued to be used since the kernel was only looking
at ET_DYN. However, since ELF_ET_DYN_BASE is traditionally set at the
top 1/3rd of the TASK_SIZE, a substantial portion of the address space
is unused.
For 32-bit tasks when RLIMIT_STACK is set to RLIM_INFINITY, programs are
loaded above the mmap region. This means they can be made to collide
(CVE-2017-1000370) or nearly collide (CVE-2017-1000371) with
pathological stack regions.
Lowering ELF_ET_DYN_BASE solves both by moving programs below the mmap
region in all cases, and will now additionally avoid programs falling
back to the mmap region by enforcing MAP_FIXED for program loads (i.e.
if it would have collided with the stack, now it will fail to load
instead of falling back to the mmap region).
To allow for a lower ELF_ET_DYN_BASE, loaders (ET_DYN without INTERP)
are loaded into the mmap region, leaving space available for either an
ET_EXEC binary with a fixed location or PIE being loaded into mmap by
the loader. Only PIE programs are loaded offset from ELF_ET_DYN_BASE,
which means architectures can now safely lower their values without risk
of loaders colliding with their subsequently loaded programs.
For 64-bit, ELF_ET_DYN_BASE is best set to 4GB to allow runtimes to use
the entire 32-bit address space for 32-bit pointers.
Thanks to PaX Team, Daniel Micay, and Rik van Riel for inspiration and
suggestions on how to implement this solution.
Fixes:
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|---|---|---|
| .. | ||
| alpha | ||
| arc | ||
| arm | ||
| arm64 | ||
| blackfin | ||
| c6x | ||
| cris | ||
| frv | ||
| h8300 | ||
| hexagon | ||
| ia64 | ||
| m32r | ||
| m68k | ||
| metag | ||
| microblaze | ||
| mips | ||
| mn10300 | ||
| nios2 | ||
| openrisc | ||
| parisc | ||
| powerpc | ||
| s390 | ||
| score | ||
| sh | ||
| sparc | ||
| tile | ||
| um | ||
| unicore32 | ||
| x86 | ||
| xtensa | ||
| .gitignore | ||
| Kconfig | ||