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Subject[kernel-hardening] [RFC V2 3/6] lib: vsprintf: physical address kernel pointer filtering options
Date
Add the kptr_restrict setting of 4 which results in %pa and
%p[rR] values being cleansed.

Address types printed with %pa are replaced by zeros. Resources printed
with %p[rR] have the starting address replaced by zeros, resource size
is still shown.

Signed-off-by: Tobin C. Harding <me@tobin.cc>
---
Documentation/sysctl/kernel.txt | 5 +++++
kernel/sysctl.c | 3 +--
lib/vsprintf.c | 31 +++++++++++++++++++++++++++++--
3 files changed, 35 insertions(+), 4 deletions(-)

diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
index 7ee183af..b6d45bc 100644
--- a/Documentation/sysctl/kernel.txt
+++ b/Documentation/sysctl/kernel.txt
@@ -398,6 +398,11 @@ When kptr_restrict is set to (3), kernel pointers printed using
%p and %pK will be replaced with 0's regardless of privileges,
however kernel pointers printed using %pP will continue to be printed.

+When kptr_restrict is set to (4), kernel pointers printed with
+%p, %pK, %pa, and %p[rR] will be replaced with 0's regardless of
+privileges. Kernel pointers printed using %pP will continue to be
+printed.
+
==============================================================

l2cr: (PPC only)
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 37ba637..f777b32 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -129,7 +129,6 @@ static unsigned long one_ul = 1;
static int one_hundred = 100;
static int one_thousand = 1000;
#ifdef CONFIG_PRINTK
-static int three = 3;
static int ten_thousand = 10000;
#endif
#ifdef CONFIG_PERF_EVENTS
@@ -852,7 +851,7 @@ static struct ctl_table kern_table[] = {
.mode = 0644,
.proc_handler = proc_dointvec_minmax_sysadmin,
.extra1 = &zero,
- .extra2 = &three,
+ .extra2 = &four,
},
#endif
{
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index e6eace0..0271223 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -406,6 +406,22 @@ static inline int kptr_restrict_cleanse_kernel_pointers(void)
return kptr_restrict >= 3;
}

+/*
+ * return non-zero if we should cleanse pointers for %pa* specifiers.
+ */
+static inline int kptr_restrict_cleanse_addresses(void)
+{
+ return kptr_restrict >= 4;
+}
+
+/*
+ * return non-zero if we should cleanse pointers for %p[rR] specifiers.
+ */
+static inline int kptr_restrict_cleanse_resources(void)
+{
+ return kptr_restrict >= 4;
+}
+
static noinline_for_stack
char *number(char *buf, char *end, unsigned long long num,
struct printf_spec spec)
@@ -758,6 +774,7 @@ char *resource_string(char *buf, char *end, struct resource *res,

char *p = sym, *pend = sym + sizeof(sym);
int decode = (fmt[0] == 'R') ? 1 : 0;
+ int cleanse = kptr_restrict_cleanse_resources();
const struct printf_spec *specp;

*p++ = '[';
@@ -785,10 +802,11 @@ char *resource_string(char *buf, char *end, struct resource *res,
p = string(p, pend, "size ", str_spec);
p = number(p, pend, resource_size(res), *specp);
} else {
- p = number(p, pend, res->start, *specp);
+ p = number(p, pend, cleanse ? 0UL : res->start, *specp);
if (res->start != res->end) {
*p++ = '-';
- p = number(p, pend, res->end, *specp);
+ p = number(p, pend, cleanse ?
+ res->end - res->start : res->end, *specp);
}
}
if (decode) {
@@ -1391,6 +1409,9 @@ char *address_val(char *buf, char *end, const void *addr, const char *fmt)
break;
}

+ if (kptr_restrict_cleanse_addresses())
+ num = 0UL;
+
return special_hex_number(buf, end, num, size);
}

@@ -1714,6 +1735,12 @@ char *device_node_string(char *buf, char *end, struct device_node *dn,
* pointer to the real address.
*
* Note: That for kptr_restrict set to 3, %p and %pK have the same meaning.
+ *
+ * Note: That for kptr_restrict set to 4, %pa will null out the physical
+ * address.
+ *
+ * Note: That for kptr_restrict set to 4, %p[rR] will null out the memory
+ * address.
*/
static noinline_for_stack
char *pointer(const char *fmt, char *buf, char *end, void *ptr,
--
2.7.4
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