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99 lines
3.6 KiB
99 lines
3.6 KiB
#include <sys/syscall.h>
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#include <sys/mman.h>
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#include <unistd.h>
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#include <fcntl.h>
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#include <errno.h>
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#define IFUNC_PREFIX _$ifun__
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#define IFUNC_IMPL_PREFIX _$impl__
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#include "ifunc.h"
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#include <memfd_secret.h>
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#define READ_ONCE(slot) ((__typeof__(slot))(*(const volatile __typeof__(slot)*)&(slot)))
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#define WRITE_ONCE(slot, value) (*((volatile __typeof__(slot)*)&(slot)) = (value))
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__attribute__((gnu_inline/*, always_inline*/))
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static inline
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int _memfd_secret_raw(unsigned int flags)
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{
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return syscall(SYS_memfd_secret, flags);
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}
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int _memfd_secret(unsigned int flags)
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{
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return _memfd_secret_raw(flags);
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}
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__attribute__((gnu_inline))
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static inline
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int _has_memfd_secret_raw()
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{
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// Attempt syscall
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int fd = _memfd_secret(0); //XXX: NOTE: man page says `FD_CLOEXEC` is a valid flag, but using it returns `EINVAL`?
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// If failure to create new fd was caused by `ENOSYS`, it is not available.
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if(fd < 0 && errno == ENOSYS)
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return 0;
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// If `fd` returned was valid, close it.
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else if(fd >= 0) close(fd);
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return 1;
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}
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static int _$has_memfd_secret = -1; //XXX: I don't think this needs to be _Atomic... But it might... (TODO: Maybe change this to use `call_once()` instead?)
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// NOTE: Making this `static` visible to TU allows IFUNC resolver to also set it, and therefore `_has_memfd_secret_raw()` may never need to be called. (XXX: Unless resolver itself calls `_has_memfd_secret()` (below V) in which case the exposure isn't needed and this can be moved back to the function body as `has` to de-clutter TU namespace a bit.)
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int _has_memfd_secret() {
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#define has _$has_memfd_secret
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int ok;
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if(__builtin_expect( (ok = READ_ONCE(has)) == -1, 0)) {
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ok = _has_memfd_secret_raw();
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WRITE_ONCE(has, ok);
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//TODO: How to add memory barrier after `WRITE_ONCE()` call? Look up GCC's memory barrier builtin. (XXX: If we're doing that, we may as well do as said above and change this to use `call_once()` to set or a `relaxed` atomic, idk... This function shouldn't be called much anyway, so.
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return ok;
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}
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#undef has
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return ok;
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}
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int IFUNC_DEF(memfd_secret, (unsigned int));
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/// Set as IFUNC target for systems with `memfd_secret()` support enabled.
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__attribute__((visibility("hidden")))
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int IFUNC_IMPL(memfd_secret, $enabled) (unsigned int flags)
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{
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return _memfd_secret_raw(flags);
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}
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/// Set as IFUNC target for systems *without* `memfd_secret()` support enabled.
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///
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/// The call is forwarded to `memfd_create()` instead.
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__attribute__((visibility("hidden")))
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int IFUNC_IMPL(memfd_secret, $disabled) (unsigned int flags)
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{
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// Translate mask `flags`, from `FD_CLOEXEC` (if it is set) -> `MEMFD_CLOEXEC`.
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if( FD_CLOEXEC != MFD_CLOEXEC ) { // NOTE: This is a constant expression, and this code will be removed if they are equal.
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// Check if all bit(s) of `FD_CLOEXEC` is in `flags`.
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if((flags & FD_CLOEXEC) == FD_CLOEXEC) {
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// Mask out the `FD_CLOEXEC` bit(s)
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flags &= ~FD_CLOEXEC;
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// Mask in the `MFD_CLOEXEC` bit(s)
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flags |= MFD_CLOEXEC;
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} // NOTE: We do not need to check cases where `flags & FD_CLOEXEC` is non-zero but the above branch is not hit, that would be an invalid call anyway. Plus I highly doubt any system will set `FD_CLOEXEC` to be more than 1 set bit anyway.
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}
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return memfd_create("memfd_secret@?", flags);
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}
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int IFUNC_RESOLVER(memfd_secret) (unsigned int flags)
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{
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return _has_memfd_secret()
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? &IFUNC_NAME(memfd_secret, $enabled)
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: &IFUNC_NAME(memfd_secret, $disabled);
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}
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//TODO: IFUNC resolver for `memfd_secret()` (Above two targets^^)
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//TODO: Use `ifunc.h`'s macros for defining the ifunc instead of manually, it de-clutters shit and removed repetition.
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