Draft: Fix dynrela func pointers on x86 and ppc64le#1448
Closed
joe-lawrence wants to merge 3 commits intodynup:masterfrom
Closed
Draft: Fix dynrela func pointers on x86 and ppc64le#1448joe-lawrence wants to merge 3 commits intodynup:masterfrom
joe-lawrence wants to merge 3 commits intodynup:masterfrom
Conversation
Various kernel arch/compiler/configuration combintions have started using the -fpatchable-function-entry compiler option to generate the padding space for fentry hooking. The full option =N[,M] will: Generate N NOPs right at the beginning of each function, with the function entry point before the Mth NOP. If M is omitted, it defaults to 0 so the function entry points to the address just at the first NOP. Cases which specify non-zero M NOPs will result in function entries offset from their section start (when building with -ffunction-sections) by some number of bytes. This value is important for create-diff-object when considering expected symbol offsets. Architecture notes as of upstream v6.14: - arm64 sets M to 2 (8 bytes total) for CONFIG_DYNAMIC_FTRACE_WITH_CALL_OPS - loongarch doesn't set M - powerpc only sets M for ppc32 - riscv doesn't set M - s390x doesn't use -fpatchable-function-entry - x86_64 sets M to CONFIG_FUNCTION_PADDING_BYTES for CONFIG_CALL_PADDING Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
With -mcmodel=small|medium on ppc64le, GCC generates an entry point
prolog like:
0000000000000000 <cmdline_proc_open>:
0: 00 00 4c 3c addis r2,r12,0
0: R_PPC64_REL16_HA .TOC.
4: 00 00 42 38 addi r2,r2,0
4: R_PPC64_REL16_LO .TOC.+0x4
But with -mcmodel=large on ppc64le, GCC generates an entry point prolog
like:
0000000000000000 <cmdline_proc_show-0x8>:
...
0: R_PPC64_REL64 .TOC.-0x8
0000000000000008 <cmdline_proc_show>:
8: f8 ff 4c e8 ld r2,-8(r12)
8: R_PPC64_ENTRY *ABS*
c: 14 62 42 7c add r2,r2,r12
In the small/medium memory model version, a function pointer relocation
can be verified by comparing the relocation types (R_PPC64_TOC16_HA or
R_PPC64_TOC16_LO_DS) and that the rela_toc->addend ==
rela_toc->sym->sym.st_value.
In the large memory module case, a function pointer can be verified by
its type (R_PPC64_ADDR64) and whether there exists a R_PPC64_ENTRY
relocation at the location its addend and symbol value point to in the
target .text section.
Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
Add an integration test to verify klp-relocation replacement of certain function pointers. In this test, the livepatch's function pointer to uptime_proc_show should resolve to the original found in the kernel and not the instance from the livepatch itself. Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
joe-lawrence
force-pushed
the
fix-dynrela-func-pointers
branch
from
bf40acf to
e48c770
Compare
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
1 participant
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
This patchset aims to resolve two issues in kpatch-build's conversion of function pointers to klp-relocations:
Finally, add a simple function pointer integration test (rather than a precompiled unit test) so that we exercise the compilation of the function pointers that kpatch-build will translate into klp-relocations. This should have detected these problems when they first appeared on supported configurations..