We are going to check the address using probe_kernel_address(). It will
be more expensive and it does not make sense for well known address.

This patch splits the string() function. The variant without the check
is then used on locations that handle string constants or strings defined
as local variables.

This patch does not change the existing behavior.

Signed-off-by: Petr Mladek <pmla...@suse.com>
---
 lib/vsprintf.c | 79 ++++++++++++++++++++++++++++++++--------------------------
 1 file changed, 43 insertions(+), 36 deletions(-)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 9ade2c4f21ba..dd71738d7a09 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -582,14 +582,11 @@ char *widen_string(char *buf, int n, char *end, struct 
printf_spec spec)
 }
 
 static noinline_for_stack
-char *string(char *buf, char *end, const char *s, struct printf_spec spec)
+char *__string(char *buf, char *end, const char *s, struct printf_spec spec)
 {
        int len = 0;
        size_t lim = spec.precision;
 
-       if ((unsigned long)s < PAGE_SIZE)
-               s = "(null)";
-
        while (lim--) {
                char c = *s++;
                if (!c)
@@ -602,6 +599,16 @@ char *string(char *buf, char *end, const char *s, struct 
printf_spec spec)
        return widen_string(buf, len, end, spec);
 }
 
+static noinline_for_stack
+char *string(char *buf, char *end, const char *s,
+                  struct printf_spec spec)
+{
+       if ((unsigned long)s < PAGE_SIZE)
+               s = "(null)";
+
+       return __string(buf, end, s, spec);
+}
+
 static bool have_filled_random_ptr_key __read_mostly;
 static siphash_key_t ptr_key __read_mostly;
 
@@ -646,7 +653,7 @@ static char *ptr_to_id(char *buf, char *end,
        if (unlikely(!have_filled_random_ptr_key)) {
                spec.field_width = default_width;
                /* string length must be less than default_width */
-               return string(buf, end, "(ptrval)", spec);
+               return __string(buf, end, "(ptrval)", spec);
        }
 
 #ifdef CONFIG_64BIT
@@ -755,7 +762,7 @@ char *symbol_string(char *buf, char *end, void *ptr,
        else
                sprint_symbol_no_offset(sym, value);
 
-       return string(buf, end, sym, spec);
+       return __string(buf, end, sym, spec);
 #else
        return special_hex_number(buf, end, value, sizeof(void *));
 #endif
@@ -821,27 +828,27 @@ char *resource_string(char *buf, char *end, struct 
resource *res,
 
        *p++ = '[';
        if (res->flags & IORESOURCE_IO) {
-               p = string(p, pend, "io  ", str_spec);
+               p = __string(p, pend, "io  ", str_spec);
                specp = &io_spec;
        } else if (res->flags & IORESOURCE_MEM) {
-               p = string(p, pend, "mem ", str_spec);
+               p = __string(p, pend, "mem ", str_spec);
                specp = &mem_spec;
        } else if (res->flags & IORESOURCE_IRQ) {
-               p = string(p, pend, "irq ", str_spec);
+               p = __string(p, pend, "irq ", str_spec);
                specp = &dec_spec;
        } else if (res->flags & IORESOURCE_DMA) {
-               p = string(p, pend, "dma ", str_spec);
+               p = __string(p, pend, "dma ", str_spec);
                specp = &dec_spec;
        } else if (res->flags & IORESOURCE_BUS) {
-               p = string(p, pend, "bus ", str_spec);
+               p = __string(p, pend, "bus ", str_spec);
                specp = &bus_spec;
        } else {
-               p = string(p, pend, "??? ", str_spec);
+               p = __string(p, pend, "??? ", str_spec);
                specp = &mem_spec;
                decode = 0;
        }
        if (decode && res->flags & IORESOURCE_UNSET) {
-               p = string(p, pend, "size ", str_spec);
+               p = __string(p, pend, "size ", str_spec);
                p = number(p, pend, resource_size(res), *specp);
        } else {
                p = number(p, pend, res->start, *specp);
@@ -852,21 +859,21 @@ char *resource_string(char *buf, char *end, struct 
resource *res,
        }
        if (decode) {
                if (res->flags & IORESOURCE_MEM_64)
-                       p = string(p, pend, " 64bit", str_spec);
+                       p = __string(p, pend, " 64bit", str_spec);
                if (res->flags & IORESOURCE_PREFETCH)
-                       p = string(p, pend, " pref", str_spec);
+                       p = __string(p, pend, " pref", str_spec);
                if (res->flags & IORESOURCE_WINDOW)
-                       p = string(p, pend, " window", str_spec);
+                       p = __string(p, pend, " window", str_spec);
                if (res->flags & IORESOURCE_DISABLED)
-                       p = string(p, pend, " disabled", str_spec);
+                       p = __string(p, pend, " disabled", str_spec);
        } else {
-               p = string(p, pend, " flags ", str_spec);
+               p = __string(p, pend, " flags ", str_spec);
                p = number(p, pend, res->flags, flag_spec);
        }
        *p++ = ']';
        *p = '\0';
 
-       return string(buf, end, sym, spec);
+       return __string(buf, end, sym, spec);
 }
 
 static noinline_for_stack
@@ -1037,7 +1044,7 @@ char *mac_address_string(char *buf, char *end, u8 *addr,
        }
        *p = '\0';
 
-       return string(buf, end, mac_addr, spec);
+       return __string(buf, end, mac_addr, spec);
 }
 
 static noinline_for_stack
@@ -1200,7 +1207,7 @@ char *ip6_addr_string(char *buf, char *end, const u8 
*addr,
        else
                ip6_string(ip6_addr, addr, fmt);
 
-       return string(buf, end, ip6_addr, spec);
+       return __string(buf, end, ip6_addr, spec);
 }
 
 static noinline_for_stack
@@ -1211,7 +1218,7 @@ char *ip4_addr_string(char *buf, char *end, const u8 
*addr,
 
        ip4_string(ip4_addr, addr, fmt);
 
-       return string(buf, end, ip4_addr, spec);
+       return __string(buf, end, ip4_addr, spec);
 }
 
 static noinline_for_stack
@@ -1273,7 +1280,7 @@ char *ip6_addr_string_sa(char *buf, char *end, const 
struct sockaddr_in6 *sa,
        }
        *p = '\0';
 
-       return string(buf, end, ip6_addr, spec);
+       return __string(buf, end, ip6_addr, spec);
 }
 
 static noinline_for_stack
@@ -1308,7 +1315,7 @@ char *ip4_addr_string_sa(char *buf, char *end, const 
struct sockaddr_in *sa,
        }
        *p = '\0';
 
-       return string(buf, end, ip4_addr, spec);
+       return __string(buf, end, ip4_addr, spec);
 }
 
 static noinline_for_stack
@@ -1409,7 +1416,7 @@ char *uuid_string(char *buf, char *end, const u8 *addr,
 
        *p = 0;
 
-       return string(buf, end, uuid, spec);
+       return __string(buf, end, uuid, spec);
 }
 
 int kptr_restrict __read_mostly;
@@ -1437,7 +1444,7 @@ char *restricted_pointer(char *buf, char *end, const void 
*ptr,
                 * because its test for CAP_SYSLOG would be meaningless.
                 */
                if (in_irq() || in_serving_softirq() || in_nmi())
-                       return string(buf, end, "pK-error", spec);
+                       return __string(buf, end, "pK-error", spec);
 
                /*
                 * Only print the real pointer value if the current
@@ -1613,13 +1620,13 @@ char *device_node_gen_full_name(const struct 
device_node *np, char *buf, char *e
 
        /* special case for root node */
        if (!parent)
-               return string(buf, end, "/", strspec);
+               return __string(buf, end, "/", strspec);
 
        for (depth = 0; parent->parent; depth++)
                parent = parent->parent;
 
        for ( ; depth >= 0; depth--) {
-               buf = string(buf, end, "/", strspec);
+               buf = __string(buf, end, "/", strspec);
                buf = string(buf, end, device_node_name_for_depth(np, depth),
                             strspec);
        }
@@ -1647,10 +1654,10 @@ char *device_node_string(char *buf, char *end, struct 
device_node *dn,
        str_spec.field_width = -1;
 
        if (!IS_ENABLED(CONFIG_OF))
-               return string(buf, end, "(!OF)", spec);
+               return __string(buf, end, "(!OF)", spec);
 
        if ((unsigned long)dn < PAGE_SIZE)
-               return string(buf, end, "(null)", spec);
+               return __string(buf, end, "(null)", spec);
 
        /* simple case without anything any more format specifiers */
        fmt++;
@@ -1686,7 +1693,7 @@ char *device_node_string(char *buf, char *end, struct 
device_node *dn,
                        tbuf[2] = of_node_check_flag(dn, OF_POPULATED) ? 'P' : 
'-';
                        tbuf[3] = of_node_check_flag(dn, OF_POPULATED_BUS) ? 
'B' : '-';
                        tbuf[4] = 0;
-                       buf = string(buf, end, tbuf, str_spec);
+                       buf = __string(buf, end, tbuf, str_spec);
                        break;
                case 'c':       /* major compatible string */
                        ret = of_property_read_string(dn, "compatible", &p);
@@ -1697,10 +1704,10 @@ char *device_node_string(char *buf, char *end, struct 
device_node *dn,
                        has_mult = false;
                        of_property_for_each_string(dn, "compatible", prop, p) {
                                if (has_mult)
-                                       buf = string(buf, end, ",", str_spec);
-                               buf = string(buf, end, "\"", str_spec);
+                                       buf = __string(buf, end, ",", str_spec);
+                               buf = __string(buf, end, "\"", str_spec);
                                buf = string(buf, end, p, str_spec);
-                               buf = string(buf, end, "\"", str_spec);
+                               buf = __string(buf, end, "\"", str_spec);
 
                                has_mult = true;
                        }
@@ -1857,7 +1864,7 @@ char *pointer(const char *fmt, char *buf, char *end, void 
*ptr,
                 */
                if (spec.field_width == -1)
                        spec.field_width = default_width;
-               return string(buf, end, "(null)", spec);
+               return __string(buf, end, "(null)", spec);
        }
 
        switch (*fmt) {
@@ -1913,7 +1920,7 @@ char *pointer(const char *fmt, char *buf, char *end, void 
*ptr,
                        case AF_INET6:
                                return ip6_addr_string_sa(buf, end, &sa->v6, 
spec, fmt);
                        default:
-                               return string(buf, end, "(invalid address)", 
spec);
+                               return __string(buf, end, "(invalid address)", 
spec);
                        }}
                }
                break;
-- 
2.13.6

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