- We load the kernel at 0x200000. Memory below that address need not be executable.
- Remove references to the .ldata section and related sections. They were just copied from the default GNU ld linker script, but we now use lld (which doesn't embed a default linker script(!)) and we are not going to use ldata anytime soon anyway.
- Pad the .bss to a 2MB boundary, like we do between .text and .data. This forces the loader to load additional files starting at a different 2MB page. Doing so allows us to keep using superpage mappings for data.
- Map memory above the kernel with NX. The kernel linker will be modified to use pmap_change_prot() to request execute access. Other preloaded data (/boot/entropy, CPU microcode, etc.) need not be mapped with execute permissions.
Details
Details
- Reviewers
alc kib - Commits
- rS353731: Tighten mapping protections on preloaded files on amd64.
Diff Detail
Diff Detail
- Repository
- rS FreeBSD src repository - subversion
- Lint
Lint Not Applicable - Unit
Tests Not Applicable
Event Timeline
| sys/conf/ldscript.amd64 | ||
|---|---|---|
| 178 ↗ | (On Diff #62801) | I disgree with this. .bss is the natural part of .data, I do not see why should they be teared apart. Esp. because we do not mmap the .data part for kernel. |
| sys/conf/ldscript.amd64 | ||
|---|---|---|
| 178 ↗ | (On Diff #62801) | I am not tearing them apart - the padding is inserted after .bss, which follows .data. |
| sys/conf/ldscript.amd64 | ||
|---|---|---|
| 178 ↗ | (On Diff #62801) | Yes, I misread the patch. Sorry. |