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kmod: maintain syscall metadata sections in kpatch syscall macros #1376

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Mar 6, 2024
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kmod: maintain syscall metadata sections in kpatch syscall macros #1376

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18 changes: 14 additions & 4 deletions kmod/patch/kpatch-syscall.h
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Original file line number Diff line number Diff line change
Expand Up @@ -15,14 +15,24 @@
* being a 'kpatch' prefix added to the __do_sys##name() function name. This
* causes kpatch-build to treat it as a new function (due to
* its new name), and its caller __se_sys##name() function is inlined by its own
* caller __x64_sys##name() function, which has an fentry hook.

* caller __x64_sys##name() function, which has an fentry hook. Since the
* kpatch versions do not provide SYSCALL_METADATA, specifically entries in the
* __syscalls_metadata and _ftrace_events sections, provide dummy values in
* these sections and instruct kpatch-build to ignore changes to them.
*
* To patch a syscall, just replace the use of the SYSCALL_DEFINE1 (or similar)
* macro with the "KPATCH_" prefixed version.
*/

#define KPATCH_IGNORE_SYSCALL_SECTIONS \
#define KPATCH_SYSCALL_METADATA(sname) \
static struct syscall_metadata __used \
__section("__syscalls_metadata") \
*__p_syscall_meta_##sname = NULL; \
KPATCH_IGNORE_SECTION("__syscalls_metadata"); \
\
static struct trace_event_call __used \
__section("_ftrace_events") \
*__event_enter_##sname = NULL; \
KPATCH_IGNORE_SECTION("_ftrace_events")

#define KPATCH_SYSCALL_DEFINE1(name, ...) KPATCH_SYSCALL_DEFINEx(1, _##name, __VA_ARGS__)
Expand All @@ -33,7 +43,7 @@
#define KPATCH_SYSCALL_DEFINE6(name, ...) KPATCH_SYSCALL_DEFINEx(6, _##name, __VA_ARGS__)

#define KPATCH_SYSCALL_DEFINEx(x, sname, ...) \
KPATCH_IGNORE_SYSCALL_SECTIONS; \
KPATCH_SYSCALL_METADATA(sname); \
__KPATCH_SYSCALL_DEFINEx(x, sname, __VA_ARGS__)

#ifdef CONFIG_X86_64
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