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

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

[Maciej Wieczor-Retman]

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/20241024013214.129639-1-torvalds@linux-foundation.org/
[2] https://lore.kernel.org/all/20241028160917.1380714-1-alexander.shishkin@linux.intel.com/

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(-)

-- 
2.47.1

[PATCH v4 1/3] selftests/lam: Move cpu_has_la57() to use cpuinfo flag

[Maciej Wieczor-Retman]

In current form cpu_has_la57() reports platform's support for LA57
through reading the output of cpuid. A much more useful information is
whether 5-level paging is actually enabled on the running system.

Presence of the la57 flag in /proc/cpuinfo signifies that 5-level paging
was compiled into the kernel, is supported by the platform and wasn't
disabled by kernel command line argument.

Use system() with cat and grep to figure out if la57 is enabled on the
running system.

Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@intel.com>
---
Changelog v4:
- Add this patch to the series.

 tools/testing/selftests/x86/lam.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/tools/testing/selftests/x86/lam.c b/tools/testing/selftests/x86/lam.c
index 0ea4f6813930..0ac805125ab2 100644
--- a/tools/testing/selftests/x86/lam.c
+++ b/tools/testing/selftests/x86/lam.c
@@ -124,14 +124,11 @@ static inline int cpu_has_lam(void)
 	return (cpuinfo[0] & (1 << 26));
 }
 
-/* Check 5-level page table feature in CPUID.(EAX=07H, ECX=00H):ECX.[bit 16] */
 static inline int cpu_has_la57(void)
 {
-	unsigned int cpuinfo[4];
-
-	__cpuid_count(0x7, 0, cpuinfo[0], cpuinfo[1], cpuinfo[2], cpuinfo[3]);
+	int ret = !!system("cat /proc/cpuinfo | grep -wq la57\n");
 
-	return (cpuinfo[2] & (1 << 16));
+	return !ret;
 }
 
 /*
-- 
2.47.1

[PATCH v4 2/3] selftests/lam: Skip test if LAM is disabled

[Maciej Wieczor-Retman]

Until LASS is merged into the kernel [1], LAM is left disabled in the
config file. Running the LAM selftest with disabled LAM only results in
unhelpful output.

Use one of LAM syscalls() to determine whether the kernel was compiled
with LAM support (CONFIG_ADDRESS_MASKING) or not. Skip running the tests
in the latter case.

[1] https://lore.kernel.org/all/20241028160917.1380714-1-alexander.shishkin@linux.intel.com/

Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@intel.com>
---
Changelog v4:
- Add this patch to the series.

 tools/testing/selftests/x86/lam.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/tools/testing/selftests/x86/lam.c b/tools/testing/selftests/x86/lam.c
index 0ac805125ab2..5aee3e231a96 100644
--- a/tools/testing/selftests/x86/lam.c
+++ b/tools/testing/selftests/x86/lam.c
@@ -124,6 +124,14 @@ static inline int cpu_has_lam(void)
 	return (cpuinfo[0] & (1 << 26));
 }
 
+static inline int kernel_has_lam(void)
+{
+	unsigned long bits;
+
+	syscall(SYS_arch_prctl, ARCH_GET_MAX_TAG_BITS, &bits);
+	return !!bits;
+}
+
 static inline int cpu_has_la57(void)
 {
 	int ret = !!system("cat /proc/cpuinfo | grep -wq la57\n");
@@ -1183,6 +1191,11 @@ int main(int argc, char **argv)
 		return KSFT_SKIP;
 	}
 
+	if (!kernel_has_lam()) {
+		ksft_print_msg("LAM is disabled in the kernel!\n");
+		return KSFT_SKIP;
+	}
+
 	while ((c = getopt(argc, argv, "ht:")) != -1) {
 		switch (c) {
 		case 't':
-- 
2.47.1

[PATCH v4 3/3] selftests/lam: Test get_user() LAM pointer handling

[Maciej Wieczor-Retman]

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().

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.

[1] https://lore.kernel.org/all/20241024013214.129639-1-torvalds@linux-foundation.org/

Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@intel.com>
---
Changelog v4:
- Use the changed cpu_has_la57() instead of mmap() to figure out current
  paging level.
- Apply Kirill's other comments: Remove redundant always true check,
  close the ioctl file before exiting, change mapping size to PAGE_SIZE
  so it looks less odd.
- Turn this patch into a series and move some text to the cover letter.

Changelog v3:
- mmap the pointer passed to get_user to high address if 5 level paging
  is enabled and to low address if 4 level paging is enabled.

Changelog v2:
- Use mmap with HIGH_ADDR to check if we're in 5 or 4 level pagetables.

 tools/testing/selftests/x86/lam.c | 102 ++++++++++++++++++++++++++++++
 1 file changed, 102 insertions(+)

diff --git a/tools/testing/selftests/x86/lam.c b/tools/testing/selftests/x86/lam.c
index 5aee3e231a96..13bfc6e5d7e0 100644
--- a/tools/testing/selftests/x86/lam.c
+++ b/tools/testing/selftests/x86/lam.c
@@ -4,6 +4,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <sys/syscall.h>
+#include <sys/ioctl.h>
 #include <time.h>
 #include <signal.h>
 #include <setjmp.h>
@@ -43,7 +44,15 @@
 #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        (0x1FFFFUL << 47)
 
 #define LOW_ADDR                (0x1UL << 30)
 #define HIGH_ADDR               (0x3UL << 48)
@@ -375,6 +384,72 @@ static int handle_syscall(struct testcases *test)
 	return ret;
 }
 
+static int get_user_syscall(struct testcases *test)
+{
+	uint64_t ptr_address, bitmask;
+	int fd, ret = 0;
+	void *ptr;
+
+	if (cpu_has_la57()) {
+		bitmask = L5_SIGN_EXT_MASK;
+		ptr_address = HIGH_ADDR;
+	} else {
+		bitmask = L4_SIGN_EXT_MASK;
+		ptr_address = LOW_ADDR;
+	}
+
+	ptr = mmap((void *)ptr_address, PAGE_SIZE, PROT_READ | PROT_WRITE,
+		   MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, -1, 0);
+
+	if (ptr == MAP_FAILED) {
+		perror("failed to map byte to pass into get_user");
+		return 1;
+	}
+
+	if (set_lam(test->lam) != 0) {
+		ret = 2;
+		goto error;
+	}
+
+	fd = memfd_create("lam_ioctl", 0);
+	if (fd == -1) {
+		munmap(ptr, PAGE_SIZE);
+		exit(EXIT_FAILURE);
+	}
+
+	switch (test->later) {
+	case GET_USER_USER:
+		/* Control group - properly tagger user pointer */
+		ptr = (void *)set_metadata((uint64_t)ptr, test->lam);
+		break;
+	case GET_USER_KERNEL_TOP:
+		/* Kernel address with top bit cleared */
+		bitmask &= (bitmask >> 1);
+		ptr = (void *)((uint64_t)ptr | bitmask);
+		break;
+	case GET_USER_KERNEL_BOT:
+		/* Kernel address with bottom sign-extension bit cleared */
+		bitmask &= (bitmask << 1);
+		ptr = (void *)((uint64_t)ptr | bitmask);
+		break;
+	case GET_USER_KERNEL:
+		/* Try to pass a kernel address */
+		ptr = (void *)((uint64_t)ptr | bitmask);
+		break;
+	default:
+		printf("Invalid test case value passed!\n");
+		break;
+	}
+
+	if (ioctl(fd, FIOASYNC, ptr) != 0)
+		ret = 1;
+
+	close(fd);
+error:
+	munmap(ptr, PAGE_SIZE);
+	return ret;
+}
+
 int sys_uring_setup(unsigned int entries, struct io_uring_params *p)
 {
 	return (int)syscall(__NR_io_uring_setup, entries, p);
@@ -888,6 +963,33 @@ static struct testcases syscall_cases[] = {
 		.test_func = handle_syscall,
 		.msg = "SYSCALL:[Negative] Disable LAM. Dereferencing pointer with metadata.\n",
 	},
+	{
+		.later = GET_USER_USER,
+		.lam = LAM_U57_BITS,
+		.test_func = get_user_syscall,
+		.msg = "GET_USER: get_user() and pass a properly tagged user pointer.\n",
+	},
+	{
+		.later = GET_USER_KERNEL_TOP,
+		.expected = 1,
+		.lam = LAM_U57_BITS,
+		.test_func = get_user_syscall,
+		.msg = "GET_USER:[Negative] get_user() with a kernel pointer and the top bit cleared.\n",
+	},
+	{
+		.later = GET_USER_KERNEL_BOT,
+		.expected = 1,
+		.lam = LAM_U57_BITS,
+		.test_func = get_user_syscall,
+		.msg = "GET_USER:[Negative] get_user() with a kernel pointer and the bottom sign-extension bit cleared.\n",
+	},
+	{
+		.later = GET_USER_KERNEL,
+		.expected = 1,
+		.lam = LAM_U57_BITS,
+		.test_func = get_user_syscall,
+		.msg = "GET_USER:[Negative] get_user() and pass a kernel pointer.\n",
+	},
 };
 
 static struct testcases mmap_cases[] = {
-- 
2.47.1

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

[Shuah Khan]

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/20241024013214.129639-1-torvalds@linux-foundation.org/
> [2] https://lore.kernel.org/all/20241028160917.1380714-1-alexander.shishkin@linux.intel.com/
> 
> 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 <skhan@linuxfoundation.org>

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

thanks,
-- Shuah

Re: [PATCH v4 1/3] selftests/lam: Move cpu_has_la57() to use cpuinfo flag

[Kirill A. Shutemov]

On Tue, Nov 26, 2024 at 02:34:48PM +0100, Maciej Wieczor-Retman wrote:
> In current form cpu_has_la57() reports platform's support for LA57
> through reading the output of cpuid. A much more useful information is
> whether 5-level paging is actually enabled on the running system.
> 
> Presence of the la57 flag in /proc/cpuinfo signifies that 5-level paging
> was compiled into the kernel, is supported by the platform and wasn't
> disabled by kernel command line argument.
> 
> Use system() with cat and grep to figure out if la57 is enabled on the
> running system.
> 
> Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@intel.com>
> ---
> Changelog v4:
> - Add this patch to the series.
> 
>  tools/testing/selftests/x86/lam.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/tools/testing/selftests/x86/lam.c b/tools/testing/selftests/x86/lam.c
> index 0ea4f6813930..0ac805125ab2 100644
> --- a/tools/testing/selftests/x86/lam.c
> +++ b/tools/testing/selftests/x86/lam.c
> @@ -124,14 +124,11 @@ static inline int cpu_has_lam(void)
>  	return (cpuinfo[0] & (1 << 26));
>  }
>  
> -/* Check 5-level page table feature in CPUID.(EAX=07H, ECX=00H):ECX.[bit 16] */
>  static inline int cpu_has_la57(void)
>  {
> -	unsigned int cpuinfo[4];
> -
> -	__cpuid_count(0x7, 0, cpuinfo[0], cpuinfo[1], cpuinfo[2], cpuinfo[3]);
> +	int ret = !!system("cat /proc/cpuinfo | grep -wq la57\n");

Heh. grep can read files on its own :P

	return !system("grep -wq la57 /proc/cpuinfo");

>  
> -	return (cpuinfo[2] & (1 << 16));
> +	return !ret;
>  }
>  
>  /*
> -- 
> 2.47.1
> 

-- 
  Kiryl Shutsemau / Kirill A. Shutemov

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

[Kirill A. Shutemov]

On Tue, Nov 26, 2024 at 02:34:47PM +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.
> 
> 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/20241024013214.129639-1-torvalds@linux-foundation.org/
> [2] https://lore.kernel.org/all/20241028160917.1380714-1-alexander.shishkin@linux.intel.com/
> 
> 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(-)

Apart from the nitpick in 1/3, looks good to me:

Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

-- 
  Kiryl Shutsemau / Kirill A. Shutemov

Re: [PATCH v4 1/3] selftests/lam: Move cpu_has_la57() to use cpuinfo flag

[Maciej Wieczor-Retman]

On 2024-11-27 at 14:11:38 +0200, Kirill A. Shutemov wrote:
>On Tue, Nov 26, 2024 at 02:34:48PM +0100, Maciej Wieczor-Retman wrote:
>> In current form cpu_has_la57() reports platform's support for LA57
>> through reading the output of cpuid. A much more useful information is
>> whether 5-level paging is actually enabled on the running system.
>> 
>> Presence of the la57 flag in /proc/cpuinfo signifies that 5-level paging
>> was compiled into the kernel, is supported by the platform and wasn't
>> disabled by kernel command line argument.
>> 
>> Use system() with cat and grep to figure out if la57 is enabled on the
>> running system.
>> 
>> Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@intel.com>
>> ---
>> Changelog v4:
>> - Add this patch to the series.
>> 
>>  tools/testing/selftests/x86/lam.c | 7 ++-----
>>  1 file changed, 2 insertions(+), 5 deletions(-)
>> 
>> diff --git a/tools/testing/selftests/x86/lam.c b/tools/testing/selftests/x86/lam.c
>> index 0ea4f6813930..0ac805125ab2 100644
>> --- a/tools/testing/selftests/x86/lam.c
>> +++ b/tools/testing/selftests/x86/lam.c
>> @@ -124,14 +124,11 @@ static inline int cpu_has_lam(void)
>>  	return (cpuinfo[0] & (1 << 26));
>>  }
>>  
>> -/* Check 5-level page table feature in CPUID.(EAX=07H, ECX=00H):ECX.[bit 16] */
>>  static inline int cpu_has_la57(void)
>>  {
>> -	unsigned int cpuinfo[4];
>> -
>> -	__cpuid_count(0x7, 0, cpuinfo[0], cpuinfo[1], cpuinfo[2], cpuinfo[3]);
>> +	int ret = !!system("cat /proc/cpuinfo | grep -wq la57\n");
>
>Heh. grep can read files on its own :P
>
>	return !system("grep -wq la57 /proc/cpuinfo");
>

Oh, thanks, missed this :)
I'll resend after fixing it.

>>  
>> -	return (cpuinfo[2] & (1 << 16));
>> +	return !ret;
>>  }
>>  
>>  /*
>> -- 
>> 2.47.1
>> 
>
>-- 
>  Kiryl Shutsemau / Kirill A. Shutemov

-- 
Kind regards
Maciej Wieczór-Retman

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

[Maciej Wieczor-Retman]

On 2024-11-26 at 09:34:36 -0700, Shuah Khan wrote:
>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/20241024013214.129639-1-torvalds@linux-foundation.org/
>> [2] https://lore.kernel.org/all/20241028160917.1380714-1-alexander.shishkin@linux.intel.com/
>> 
>> 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 <skhan@linuxfoundation.org>
>
>If you want me to take this through selftest tree, I can do that.
>
>thanks,
>-- Shuah

Thank you, yes, that'd be great!

I also just resent v5 [1] fixing the small mistake that Kirill pointed out in
"selftests/lam: Move cpu_has_la57() to use cpuinfo flag" [2]. Could you please
pull that fixed version?

[1] https://lore.kernel.org/all/cover.1732728879.git.maciej.wieczor-retman@intel.com/
[2] https://lore.kernel.org/all/6kfafs7wio7ruth3p54pezqwcultxqqpnjvehjzaz7hlba4rp3@6kb5zdqfglsl/

-- 
Kind regards
Maciej Wieczór-Retman