On 2024-10-30 at 14:31:51 +0200, Kirill A. Shutemov wrote:
>On Tue, Oct 29, 2024 at 03:14:20PM +0100, 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.
>>
>> 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.
>>
>> 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.
>>
>> [1]
>> https://lore.kernel.org/all/[email protected]/
>> [2]
>> https://lore.kernel.org/all/[email protected]/
>>
>> Signed-off-by: Maciej Wieczor-Retman
>> ---
>> tools/testing/selftests/x86/lam.c | 85 +++
>> 1 file changed, 85 insertions(+)
>>
>> diff --git a/tools/testing/selftests/x86/lam.c
>> b/tools/testing/selftests/x86/lam.c
>> index 0ea4f6813930..3c53d4b7aa61 100644
>> --- a/tools/testing/selftests/x86/lam.c
>> +++ b/tools/testing/selftests/x86/lam.c
>> @@ -4,6 +4,7 @@
>> #include
>> #include
>> #include
>> +#include
>> #include
>> #include
>> #include
>> @@ -43,10 +44,19 @@
>> #define FUNC_INHERITE 0x20
>> #define FUNC_PASID 0x40
>>
>> +/* get_user() pointer test cases */
>> +#define GET_USER_USER 0
>> +#define GET_USER_KERNEL_TOP 1
>> +#define GET_USER_KERNEL_BOT 2
>> +#define GET_USER_KERNEL 3
>> +
>> #define TEST_MASK 0x7f
>> +#define L5_SIGN_EXT_MASK(0xFFUL << 56)
>> +#define L4_SIGN_EXT_MASK(0x1UL << 47)
>>
>> #define LOW_ADDR(0x1UL << 30)
>> #define HIGH_ADDR (0x3UL << 48)
>> +#define L5_ADDR (0x1UL << 48)
>>
>> #define MALLOC_LEN 32
>>
>> @@ -370,6 +380,54 @@ static int handle_syscall(struct testcases *test)
>> return ret;
>> }
>>
>> +static int get_user_syscall(struct testcases *test)
>> +{
>> +int ret = 0;
>> +int ptr_value = 0;
>> +void *ptr = &ptr_value;
>> +int fd;
>> +
>> +uint64_t bitmask = ((uint64_t)ptr & L5_ADDR) ? L5_SIGN_EXT_MASK :
>> + L4_SIGN_EXT_MASK;
>
>Emm. Do you expect stack to be above at the very top of address space on
>5-level paging machines? It is not true. We don't allocate any memory
>above 46-bit unless asked explicitly.
Right, I'm not sure why I thought that would work here.
>See tools/testing/selftests/mm/va_high_addr_switch.c
Thanks for the tip, I'll use mmap/munmap to determine the enabled pagetable
level.
>
>--
> Kiryl Shutsemau / Kirill A. Shutemov
--
Kind regards
Maciej Wieczór-Retman
