[2/6] tunables: Add LD_HWCAP_MASK to tunables
Commit Message
Add LD_HWCAP_MASK to tunables in preparation of it being removed from
rtld.c. This allows us to read LD_HWCAP_MASK much earlier so that it
can influence IFUNC resolution in aarch64.
This patch does not actually do anything other than read the
LD_HWCAP_MASK variable and add the tunables way to set the
LD_HWCAP_MASK, i.e. via the glibc.tune.hwcap_mask tunable. In a
follow-up patch, the _dl_hwcap_mask will be replaced with
glibc.tune.hwcap_mask to complete the transition.
* elf/dl-tunables.list: Add glibc.tune.hwcap_mask.
* scripts/gen-tunables.awk: Include dl-procinfo.h.
* manual/tunables.texi: Document glibc.tune.hwcap_mask.
---
elf/dl-tunables.list | 7 +++++++
manual/tunables.texi | 23 +++++++++++++++++++++++
scripts/gen-tunables.awk | 1 +
3 files changed, 31 insertions(+)
Comments
On 01/06/2017 17:12, Siddhesh Poyarekar wrote:
> Add LD_HWCAP_MASK to tunables in preparation of it being removed from
> rtld.c. This allows us to read LD_HWCAP_MASK much earlier so that it
> can influence IFUNC resolution in aarch64.
>
> This patch does not actually do anything other than read the
> LD_HWCAP_MASK variable and add the tunables way to set the
> LD_HWCAP_MASK, i.e. via the glibc.tune.hwcap_mask tunable. In a
> follow-up patch, the _dl_hwcap_mask will be replaced with
> glibc.tune.hwcap_mask to complete the transition.
>
> * elf/dl-tunables.list: Add glibc.tune.hwcap_mask.
> * scripts/gen-tunables.awk: Include dl-procinfo.h.
> * manual/tunables.texi: Document glibc.tune.hwcap_mask.
LGTM with a remark below.
> ---
> elf/dl-tunables.list | 7 +++++++
> manual/tunables.texi | 23 +++++++++++++++++++++++
> scripts/gen-tunables.awk | 1 +
> 3 files changed, 31 insertions(+)
>
> diff --git a/elf/dl-tunables.list b/elf/dl-tunables.list
> index b9f1488..41ce9af 100644
> --- a/elf/dl-tunables.list
> +++ b/elf/dl-tunables.list
> @@ -77,4 +77,11 @@ glibc {
> security_level: SXID_IGNORE
> }
> }
> + tune {
> + hwcap_mask {
> + type: UINT_64
> + env_alias: LD_HWCAP_MASK
> + default: HWCAP_IMPORTANT
> + }
> + }
LD_HWCAP_MASK is on UNSECURE_ENVVARS at sysdeps/generic/unsecvars.h, so I think
we should add a security_level: SXID_IGNORE for hwcap_mask as well.
On 06/06/2017 14:57, Adhemerval Zanella wrote:
>
>
> On 01/06/2017 17:12, Siddhesh Poyarekar wrote:
>> Add LD_HWCAP_MASK to tunables in preparation of it being removed from
>> rtld.c. This allows us to read LD_HWCAP_MASK much earlier so that it
>> can influence IFUNC resolution in aarch64.
>>
>> This patch does not actually do anything other than read the
>> LD_HWCAP_MASK variable and add the tunables way to set the
>> LD_HWCAP_MASK, i.e. via the glibc.tune.hwcap_mask tunable. In a
>> follow-up patch, the _dl_hwcap_mask will be replaced with
>> glibc.tune.hwcap_mask to complete the transition.
>>
>> * elf/dl-tunables.list: Add glibc.tune.hwcap_mask.
>> * scripts/gen-tunables.awk: Include dl-procinfo.h.
>> * manual/tunables.texi: Document glibc.tune.hwcap_mask.
>
> LGTM with a remark below.
>
>> ---
>> elf/dl-tunables.list | 7 +++++++
>> manual/tunables.texi | 23 +++++++++++++++++++++++
>> scripts/gen-tunables.awk | 1 +
>> 3 files changed, 31 insertions(+)
>>
>> diff --git a/elf/dl-tunables.list b/elf/dl-tunables.list
>> index b9f1488..41ce9af 100644
>> --- a/elf/dl-tunables.list
>> +++ b/elf/dl-tunables.list
>> @@ -77,4 +77,11 @@ glibc {
>> security_level: SXID_IGNORE
>> }
>> }
>> + tune {
>> + hwcap_mask {
>> + type: UINT_64
>> + env_alias: LD_HWCAP_MASK
>> + default: HWCAP_IMPORTANT
>> + }
>> + }
>
> LD_HWCAP_MASK is on UNSECURE_ENVVARS at sysdeps/generic/unsecvars.h, so I think
> we should add a security_level: SXID_IGNORE for hwcap_mask as well.
>
I am getting build errors for i686 and s390{x} with --enable-tunables:
In file included from /home/azanella/Projects/glibc/build/i686-linux-gnu/dl-tunable-list.h:6:0,
from ./dl-tunables.h:67,
from ../elf/dl-sysdep.c:47,
from ../sysdeps/unix/sysv/linux/dl-sysdep.c:38:
../sysdeps/unix/sysv/linux/i386/dl-procinfo.h:25:1: error: redefinition of ‘_dl_procinfo’
_dl_procinfo (unsigned int type, unsigned long int word)
^~~~~~~~~~~~
In file included from ../elf/dl-sysdep.c:42:0,
from ../sysdeps/unix/sysv/linux/dl-sysdep.c:38:
../sysdeps/unix/sysv/linux/i386/dl-procinfo.h:25:1: note: previous definition of ‘_dl_procinfo’ was here
_dl_procinfo (unsigned int type, unsigned long int word)
^~~~~~~~~~~~
It because both Linux i686 and s390 dl-procinfo.h do not have include guard (as
for the other dl-procinfo.h implementation). I think you should include them
on this patch.
On Tuesday 06 June 2017 11:27 PM, Adhemerval Zanella wrote:
> LD_HWCAP_MASK is on UNSECURE_ENVVARS at sysdeps/generic/unsecvars.h, so I think
> we should add a security_level: SXID_IGNORE for hwcap_mask as well.
It is in UNSECURE_ENVVARS, so it should be SXID_ERASE (the default) and
not SXID_IGNORE since the latter will make the tunable available for
children of setuid processes.
Siddhesh
On 07/06/2017 02:33, Siddhesh Poyarekar wrote:
> On Tuesday 06 June 2017 11:27 PM, Adhemerval Zanella wrote:
>> LD_HWCAP_MASK is on UNSECURE_ENVVARS at sysdeps/generic/unsecvars.h, so I think
>> we should add a security_level: SXID_IGNORE for hwcap_mask as well.
>
> It is in UNSECURE_ENVVARS, so it should be SXID_ERASE (the default) and
> not SXID_IGNORE since the latter will make the tunable available for
> children of setuid processes.
Right, I wasn't aware SXID_ERASE was the default. Thanks for the clarification.
@@ -77,4 +77,11 @@ glibc {
security_level: SXID_IGNORE
}
}
+ tune {
+ hwcap_mask {
+ type: UINT_64
+ env_alias: LD_HWCAP_MASK
+ default: HWCAP_IMPORTANT
+ }
+ }
}
@@ -31,6 +31,8 @@ their own namespace.
@menu
* Tunable names:: The structure of a tunable name
* Memory Allocation Tunables:: Tunables in the memory allocation subsystem
+* Hardware Capability Tunables:: Tunables that modify the hardware
+ capabilities seen by @theglibc{}
@end menu
@node Tunable names
@@ -190,3 +192,24 @@ number of arenas is determined by the number of CPU cores online. For 32-bit
systems the limit is twice the number of cores online and on 64-bit systems, it
is 8 times the number of cores online.
@end deftp
+
+@node Hardware Capability Tunables
+@section Hardware Capability Tunables
+@cindex hardware capability tunables
+@cindex hwcap tunables
+@cindex tunables, hwcap
+
+@deftp {Tunable namespace} glibc.tune
+Behavior of @theglibc{} can be tuned to assume specific hardware capabilities
+by setting the following tunables in the @code{tune} namespace:
+@end deftp
+
+@deftp Tunable glibc.tune.hwcap_mask
+This tunable supersedes the @env{LD_HWCAP_MASK} environment variable and is
+identical in features.
+
+The @code{AT_HWCAP} key in the Auxilliary Vector specifies instruction set
+extensions available in the processor at runtime for some architectures. The
+@code{glibc.tune.hwcap_mask} tunable allows the user to mask out those
+capabilities at runtime, thus disabling use of those extensions.
+@end deftp
@@ -134,6 +134,7 @@ END {
print "# error \"Do not include this file directly.\""
print "# error \"Include tunables.h instead.\""
print "#endif"
+ print "#include <dl-procinfo.h>\n"
# Now, the enum names
print "\ntypedef enum"