[v4,0/3] selftests/lam: get_user additions and LAM enabled check

Message

Maciej Wieczor-Retman Nov. 26, 2024, 1:34 p.m. UTC

Recent change in how get_user() handles pointers [1] has a specific case
for LAM. It assigns a different bitmask that's later used to check
whether a pointer comes from userland in get_user().

While currently commented out (until LASS [2] is merged into the kernel)
it's worth making changes to the LAM selftest ahead of time.

Modify cpu_has_la57() so it provides current paging level information
instead of the cpuid one.

Add test case to LAM that utilizes a ioctl (FIOASYNC) syscall which uses
get_user() in its implementation. Execute the syscall with differently
tagged pointers to verify that valid user pointers are passing through
and invalid kernel/non-canonical pointers are not.

Also to avoid unhelpful test failures add a check in main() to skip
running tests if LAM was not compiled into the kernel.

Code was tested on a Sierra Forest Xeon machine that's LAM capable. The
test was ran without issues with both the LAM lines from [1] untouched
and commented out. The test was also ran without issues with LAM_SUP
both enabled and disabled.

4/5 level pagetables code paths were also successfully tested in Simics
on a 5-level capable machine.

[1] https://lore.kernel.org/all/[e-mail]/
[2] https://lore.kernel.org/all/[e-mail]/

Maciej Wieczor-Retman (3):
  selftests/lam: Move cpu_has_la57() to use cpuinfo flag
  selftests/lam: Skip test if LAM is disabled
  selftests/lam: Test get_user() LAM pointer handling

 tools/testing/selftests/x86/lam.c | 122 ++++++++++++++++++++++++++++--
 1 file changed, 117 insertions(+), 5 deletions(-)

Comments

Shuah Khan Nov. 26, 2024, 4:34 p.m. UTC | #1

On 11/26/24 06:34, Maciej Wieczor-Retman wrote:
> Recent change in how get_user() handles pointers [1] has a specific case
> for LAM. It assigns a different bitmask that's later used to check
> whether a pointer comes from userland in get_user().
> 
> While currently commented out (until LASS [2] is merged into the kernel)
> it's worth making changes to the LAM selftest ahead of time.
> 
> Modify cpu_has_la57() so it provides current paging level information
> instead of the cpuid one.
> 
> Add test case to LAM that utilizes a ioctl (FIOASYNC) syscall which uses
> get_user() in its implementation. Execute the syscall with differently
> tagged pointers to verify that valid user pointers are passing through
> and invalid kernel/non-canonical pointers are not.
> 
> Also to avoid unhelpful test failures add a check in main() to skip
> running tests if LAM was not compiled into the kernel.
> 
> Code was tested on a Sierra Forest Xeon machine that's LAM capable. The
> test was ran without issues with both the LAM lines from [1] untouched
> and commented out. The test was also ran without issues with LAM_SUP
> both enabled and disabled.
> 
> 4/5 level pagetables code paths were also successfully tested in Simics
> on a 5-level capable machine.
> 
> [1] https://lore.kernel.org/all/[e-mail]/
> [2] https://lore.kernel.org/all/[e-mail]/
> 
> Maciej Wieczor-Retman (3):
>    selftests/lam: Move cpu_has_la57() to use cpuinfo flag
>    selftests/lam: Skip test if LAM is disabled
>    selftests/lam: Test get_user() LAM pointer handling
> 
>   tools/testing/selftests/x86/lam.c | 122 ++++++++++++++++++++++++++++--
>   1 file changed, 117 insertions(+), 5 deletions(-)
> 

Looks good to me. For selftests if it is going through x86 tree.

Acked-by: Shuah Khan <[e-mail]>

If you want me to take this through selftest tree, I can do that.

thanks,
-- Shuah