Commit 6b06755a authored by Mario Limonciello's avatar Mario Limonciello Committed by Borislav Petkov (AMD)
Browse files

x86/amd_node: Add support for debugfs access to SMN registers 



There are certain registers on AMD Zen systems that can only be accessed
through SMN.

Introduce a new interface that provides debugfs files for accessing SMN.  As
this introduces the capability for userspace to manipulate the hardware in
unpredictable ways, taint the kernel when writing.

Signed-off-by: default avatarMario Limonciello <mario.limonciello@amd.com>
Signed-off-by: default avatarYazen Ghannam <yazen.ghannam@amd.com>
Signed-off-by: default avatarBorislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20250130-wip-x86-amd-nb-cleanup-v4-3-b5cc997e471b@amd.com
parent bebe0afb

arch/x86/kernel/amd_node.c

+99 −0
Original line number Diff line number Diff line
@@ -8,6 +8,7 @@ 
 * Author: Yazen Ghannam <Yazen.Ghannam@amd.com>

 */



#include <linux/debugfs.h>

#include <asm/amd_node.h>



/*
@@ -192,6 +193,87 @@ int __must_check amd_smn_hsmp_rdwr(u16 node, u32 address, u32 *value, bool write 
}

EXPORT_SYMBOL_GPL(amd_smn_hsmp_rdwr);



static struct dentry *debugfs_dir;

static u16 debug_node;

static u32 debug_address;



static ssize_t smn_node_write(struct file *file, const char __user *userbuf,

			      size_t count, loff_t *ppos)

{

	u16 node;

	int ret;



	ret = kstrtou16_from_user(userbuf, count, 0, &node);

	if (ret)

		return ret;



	if (node >= amd_num_nodes())

		return -ENODEV;



	debug_node = node;

	return count;

}



static int smn_node_show(struct seq_file *m, void *v)

{

	seq_printf(m, "0x%08x\n", debug_node);

	return 0;

}



static ssize_t smn_address_write(struct file *file, const char __user *userbuf,

				 size_t count, loff_t *ppos)

{

	int ret;



	ret = kstrtouint_from_user(userbuf, count, 0, &debug_address);

	if (ret)

		return ret;



	return count;

}



static int smn_address_show(struct seq_file *m, void *v)

{

	seq_printf(m, "0x%08x\n", debug_address);

	return 0;

}



static int smn_value_show(struct seq_file *m, void *v)

{

	u32 val;

	int ret;



	ret = amd_smn_read(debug_node, debug_address, &val);

	if (ret)

		return ret;



	seq_printf(m, "0x%08x\n", val);

	return 0;

}



static ssize_t smn_value_write(struct file *file, const char __user *userbuf,

			       size_t count, loff_t *ppos)

{

	u32 val;

	int ret;



	ret = kstrtouint_from_user(userbuf, count, 0, &val);

	if (ret)

		return ret;



	add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK);



	ret = amd_smn_write(debug_node, debug_address, val);

	if (ret)

		return ret;



	return count;

}



DEFINE_SHOW_STORE_ATTRIBUTE(smn_node);

DEFINE_SHOW_STORE_ATTRIBUTE(smn_address);

DEFINE_SHOW_STORE_ATTRIBUTE(smn_value);



static int amd_cache_roots(void)

{

	u16 node, num_nodes = amd_num_nodes();
@@ -239,6 +321,15 @@ static int reserve_root_config_spaces(void) 
	return 0;

}



static bool enable_dfs;



static int __init amd_smn_enable_dfs(char *str)

{

	enable_dfs = true;

	return 1;

}

__setup("amd_smn_debugfs_enable", amd_smn_enable_dfs);



static int __init amd_smn_init(void)

{

	int err;
@@ -259,6 +350,14 @@ static int __init amd_smn_init(void) 
	if (err)

		return err;



	if (enable_dfs) {

		debugfs_dir = debugfs_create_dir("amd_smn", arch_debugfs_dir);



		debugfs_create_file("node",	0600, debugfs_dir, NULL, &smn_node_fops);

		debugfs_create_file("address",	0600, debugfs_dir, NULL, &smn_address_fops);

		debugfs_create_file("value",	0600, debugfs_dir, NULL, &smn_value_fops);

	}



	return 0;

}