klibc - Jul 2020 - [PATCH] Add syscall wrappers required by libkeyutils

libkeyutils is used by the keyctl command which is required for loading
keys into the kernel (e.g. for mounting an authenticated UBIFS as root
file system).

libkeyutils usually invokes syscall() directly. As syscall() is not
provided by klibc, libkeyutils has to be slightly modified for using the
klibc wrappers.

Signed-off-by: Christian Eggers <ceggers at arri.de>
---
 usr/klibc/SYSCALLS.def | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/usr/klibc/SYSCALLS.def b/usr/klibc/SYSCALLS.def
index 461d9bf6..67056a2c 100644
--- a/usr/klibc/SYSCALLS.def
+++ b/usr/klibc/SYSCALLS.def
@@ -274,6 +274,9 @@ int reboot::__reboot(int, int, int, void *);
 int syslog::klogctl(int, char *, int);
 int sysinfo(struct sysinfo *);
 long kexec_load(void *, unsigned long, struct kexec_segment *, unsigned long);
+int add_key(const char *, const char *, const void *, size_t, int);
+int request_key(const char *, const char *, const char *, int);
+long keyctl::__keyctl(int, unsigned long, unsigned long, unsigned long,
unsigned long);
 
 /*
  * Low-level I/O (generally architecture-specific);
-- 
Christian Eggers
Embedded software developer

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On Wed, 2020-07-08 at 08:37 +0200, Christian Eggers
wrote:
> libkeyutils is used by the keyctl command which is required for loading
> keys into the kernel (e.g. for mounting an authenticated UBIFS as root
> file system).
> 
> libkeyutils usually invokes syscall() directly. As syscall() is not
> provided by klibc, libkeyutils has to be slightly modified for using the
> klibc wrappers.
Wouldn't it be more useful for klibc to implement syscall() then?

Ben.
> Signed-off-by: Christian Eggers <ceggers at arri.de>
> ---
>  usr/klibc/SYSCALLS.def | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/usr/klibc/SYSCALLS.def b/usr/klibc/SYSCALLS.def
> index 461d9bf6..67056a2c 100644
> --- a/usr/klibc/SYSCALLS.def
> +++ b/usr/klibc/SYSCALLS.def
> @@ -274,6 +274,9 @@ int reboot::__reboot(int, int, int, void *);
>  int syslog::klogctl(int, char *, int);
>  int sysinfo(struct sysinfo *);
>  long kexec_load(void *, unsigned long, struct kexec_segment *, unsigned
long);
> +int add_key(const char *, const char *, const void *, size_t, int);
> +int request_key(const char *, const char *, const char *, int);
> +long keyctl::__keyctl(int, unsigned long, unsigned long, unsigned long,
unsigned long);
>  
>  /*
>   * Low-level I/O (generally architecture-specific);
-- 
Ben Hutchings
Anthony's Law of Force: Don't force it, get a larger hammer.


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On Saturday, 25 July 2020, 23:36:33 CEST, Ben Hutchings
wrote:
> On Wed, 2020-07-08 at 08:37 +0200, Christian Eggers wrote:
> > ...
> > libkeyutils usually invokes syscall() directly. As syscall() is not
> > provided by klibc, libkeyutils has to be slightly modified for using
the
> > klibc wrappers.
>
> Wouldn't it be more useful for klibc to implement syscall() then?
I hope that somebody else could respond to this question as I am likely not
skilled enough to answer this.

For me it looks like there are currently two cases of using syscalls in klibc:
1. Exporting stubs directly: For many syscalls, automatically generated stubs
are directly exported as symbols for use by the linker. Examples: setpgid()/
getpgid()

2. Using stubs internally for implementing public function. The auto generated
stub is used as base for implementing a C library function. Example: exit()

For both cases, the code for the individual stubs is auto generated using a
perl script (with an arch specific "plugin"). All generated stubs call
common
arch specific assembly code (__syscall_common).

The lack of the syscall function itself lead me to the (probably wrong)
conclusion that this is "by design". Should all syscalls use the
generated
stubs?

There are some syscalls which are traditionally not implemented by C libraries
(like keyctl, add_key and request_key). These functions are required for
mounting encrypted / authenticated (root) file systems. Programs using this
functionality call syscall() directly. Providing a syscall function in klibc
would avoid klibc specific modifications of such software.

Are there reasons for NOT providing the syscall() function in klibc? Who is
able to implement syscall() for klibc?

regards
Christian



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Sitz: M?nchen - Registergericht: Amtsgericht M?nchen - Handelsregisternummer:
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Pers?nlich haftender Gesellschafter: Arnold & Richter Cine Technik GmbH
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HRB 54477
Gesch?ftsf?hrer: Dr. Michael Neuh?user; Stephan Schenk; Walter Trauninger;
Markus Zeiler