kpatch-build: Add support for module symbol namespaces#1467
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joe-lawrence merged 3 commits intodynup:masterfrom Jul 8, 2025
Merged
kpatch-build: Add support for module symbol namespaces#1467joe-lawrence merged 3 commits intodynup:masterfrom
joe-lawrence merged 3 commits intodynup:masterfrom
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All previous callers needed a corresponding .rela section, but the following patch just needs to create a .modinfo section. Split create_section_pair() into two parts: create the base section seperately, then add the relocation section for those who request it. Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
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(I pushed up an example obj test case here: dynup/kpatch-unit-test-objs#53 It's x86-only, but that's fine as this feature isn't architecture specific. This MR can be updated to move forward the submodule reference when that MR is approved.) |
jpoimboe
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Jul 1, 2025
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| struct section *sec; | ||
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| sec = create_section(kelf_out, ".modinfo", |
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Should this be skipped if .modinfo doesn't exist in the patched object?
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Yup, no need to create an empty section.
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Actually I suppose it should only create .modinfo if kelf_patched->modinfo_data is non-NULL?
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True, that's a better test, as it would skip instances with .modinfo but no imports.
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Kernel module namespace imports are saved in the .modinfo section in key-value strings. In order for a livepatch to access those symbols in those namespaces, it needs to provide the same imports else modpost refuses to process it. For example: ERROR: modpost: module livepatch-test uses symbol dma_buf_export from namespace DMA_BUF, but does not import it. We don't need the entire .modinfo section, as it carries other key-value pairs that we are not interested in. Selectively extract all of the "import_ns=<value" strings and then restore them in the ELF output for inclusion in the livepatch .ko. Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
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Roberto Bergantinos Corpas rbergant@redhat.com reported a problem when building a kpatch for:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/patch/?id=021ba7f1babd029e714d13a6bf2571b08af96d0f
The problem is that the livepatch needs to access symbols exported via the "DMA_BUF" symbol namespace. A workaround is to add
MODULE_IMPORT_NS("DMA_BUF")to the kpatch, but then kpatch-build complains about unhandled .modinfo changes.Update kpatch-build to allow .modinfo changes and extract the
import_ns=<value>strings from .modinfo for inclusion in the output ELF object file. Coupled withMODULE_IMPORT_NS("DMA_BUF"), this allows kpatch to build a livepatch that accesses a module symbol namespace.