[PATCH v2] kallsyms: enhance %pS/s/b printing when KALLSYSMS is disabled

[PATCH v2] kallsyms: enhance %pS/s/b printing when KALLSYSMS is disabled

[Maninder Singh]

print module information when KALLSYMS is disabled.

No change for %pB, as it needs to know symbol name to adjust address
value which can't be done without KALLSYMS.

(A) original output with KALLSYMS:
[8.842129] ps function_1 [crash]
[8.842735] pS function_1+0x4/0x2c [crash]
[8.842890] pSb function_1+0x4/0x2c [crash b367e79021b9f3b0172f9a36d4261c1f528ca1b3]
[8.843175] pB function_1+0x4/0x2c [crash]
[8.843362] pBb function_1+0x4/0x2c [crash b367e79021b9f3b0172f9a36d4261c1f528ca1b3]

(B) original output without KALLSYMS:
[12.487424] ps 0xffff800000eb008c
[12.487598] pS 0xffff800000eb008c
[12.487723] pSb 0xffff800000eb008c
[12.487850] pB 0xffff800000eb008c
[12.487967] pBb 0xffff800000eb008c

(C) With patched kernel without KALLSYMS:
[7.870286] ps 0xffff800000f2008c [crash]        // similar to original 
[7.870716] pS 0x(____ptrval____)+0x8c [crash]   // base address hashed and offset is without hash
[7.871025] pSb 0x(____ptrval____)+0x8c [crash 3423a8993a7033fb79e5add14bf9d8d6b56330ca]
[7.871321] pB 0x(____ptrval____)+0x8c [crash]
[7.871512] pBb 0x(____ptrval____)+0x8c [crash 3423a8993a7033fb79e5add14bf9d8d6b56330ca]
[7.872191] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000

with disable hashing:
[8.563916] ps 0xffff800000f2008c [crash]
[8.564574] pS 0xffff800000f20000+0x8c [crash]
[8.564749] pSb 0xffff800000f20000+0x8c [crash 3423a8993a7033fb79e5add14bf9d8d6b56330ca]
[8.565008] pB 0xffff800000f20000+0x8c [crash]
[8.565154] pBb 0xffff800000f20000+0x8c [crash 3423a8993a7033fb79e5add14bf9d8d6b56330ca]

Suggested-by: Petr Mladek <pmladek@suse.com>
Co-developed-by: Vaneet Narang <v.narang@samsung.com>
Signed-off-by: Vaneet Narang <v.narang@samsung.com>
Signed-off-by: Maninder Singh <maninder1.s@samsung.com>
---
v1->v2: hash base address of module, change *fmt to fmt[0] and removed
        copy paste.

 include/linux/kallsyms.h |  2 +
 include/linux/module.h   | 22 +++++++++++
 kernel/kallsyms.c        | 26 ++++++-------
 kernel/module.c          |  4 +-
 lib/vsprintf.c           | 84 +++++++++++++++++++++++++++++++++-------
 5 files changed, 109 insertions(+), 29 deletions(-)

diff --git a/include/linux/kallsyms.h b/include/linux/kallsyms.h
index e5ad6e31697d..c24fa627ab6e 100644
--- a/include/linux/kallsyms.h
+++ b/include/linux/kallsyms.h
@@ -89,6 +89,8 @@ extern int sprint_symbol_build_id(char *buffer, unsigned long address);
 extern int sprint_symbol_no_offset(char *buffer, unsigned long address);
 extern int sprint_backtrace(char *buffer, unsigned long address);
 extern int sprint_backtrace_build_id(char *buffer, unsigned long address);
+extern int sprint_kallsym_common(char *buffer, unsigned long address, int build_id,
+			    int backtrace, int symbol);
 
 int lookup_symbol_name(unsigned long addr, char *symname);
 int lookup_symbol_attrs(unsigned long addr, unsigned long *size, unsigned long *offset, char *modname, char *name);
diff --git a/include/linux/module.h b/include/linux/module.h
index 1e135fd5c076..26a49e663351 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -678,6 +678,22 @@ static inline bool is_livepatch_module(struct module *mod)
 bool is_module_sig_enforced(void);
 void set_module_sig_enforced(void);
 
+static inline int fill_name_build_id(char *buffer, char *modname,
+			    int add_buildid, const unsigned char *buildid,
+			    int len)
+{
+	len += sprintf(buffer + len, " [%s", modname);
+#if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID)
+	if (add_buildid && buildid) {
+		/* build ID should match length of sprintf */
+		static_assert(sizeof(typeof_member(struct module, build_id)) == 20);
+		len += sprintf(buffer + len, " %20phN", buildid);
+	}
+#endif
+	len += sprintf(buffer + len, "]");
+
+	return len;
+}
 #else /* !CONFIG_MODULES... */
 
 static inline struct module *__module_address(unsigned long addr)
@@ -818,6 +834,12 @@ void *dereference_module_function_descriptor(struct module *mod, void *ptr)
 	return ptr;
 }
 
+static inline int fill_name_build_id(char *buffer, char *modname,
+			    int add_buildid, const unsigned char *buildid,
+			    int len)
+{
+	return 0;
+}
 #endif /* CONFIG_MODULES */
 
 #ifdef CONFIG_SYSFS
diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index 57213e1d2349..cdbcaf86252a 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -479,19 +479,8 @@ static int __sprint_symbol(char *buffer, unsigned long address,
 	if (add_offset)
 		len += sprintf(buffer + len, "+%#lx/%#lx", offset, size);
 
-	if (modname) {
-		len += sprintf(buffer + len, " [%s", modname);
-#if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID)
-		if (add_buildid && buildid) {
-			/* build ID should match length of sprintf */
-#if IS_ENABLED(CONFIG_MODULES)
-			static_assert(sizeof(typeof_member(struct module, build_id)) == 20);
-#endif
-			len += sprintf(buffer + len, " %20phN", buildid);
-		}
-#endif
-		len += sprintf(buffer + len, "]");
-	}
+	if (modname)
+		len += fill_name_build_id(buffer, modname, add_buildid, buildid, len);
 
 	return len;
 }
@@ -586,6 +575,17 @@ int sprint_backtrace_build_id(char *buffer, unsigned long address)
 	return __sprint_symbol(buffer, address, -1, 1, 1);
 }
 
+int sprint_kallsym_common(char *buffer, unsigned long address, int build_id,
+			    int backtrace, int symbol)
+{
+	if (backtrace)
+		return __sprint_symbol(buffer, address, -1, 1, build_id);
+	else if (symbol)
+		return __sprint_symbol(buffer, address, 0, 1, build_id);
+	else
+		return __sprint_symbol(buffer, address, 0, 0, 0);
+}
+
 /* To avoid using get_symbol_offset for every symbol, we carry prefix along. */
 struct kallsym_iter {
 	loff_t pos;
diff --git a/kernel/module.c b/kernel/module.c
index 6cea788fd965..5756d31a024b 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -1465,12 +1465,10 @@ resolve_symbol_wait(struct module *mod,
 	return ksym;
 }
 
-#ifdef CONFIG_KALLSYMS
 static inline bool sect_empty(const Elf_Shdr *sect)
 {
 	return !(sect->sh_flags & SHF_ALLOC) || sect->sh_size == 0;
 }
-#endif
 
 /*
  * /sys/module/foo/sections stuff
@@ -2799,7 +2797,7 @@ static void add_kallsyms(struct module *mod, const struct load_info *info)
 }
 #endif /* CONFIG_KALLSYMS */
 
-#if IS_ENABLED(CONFIG_KALLSYMS) && IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID)
+#if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID)
 static void init_build_id(struct module *mod, const struct load_info *info)
 {
 	const Elf_Shdr *sechdr;
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 7adb8fd4d804..064b0cc45a37 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -1000,33 +1000,91 @@ char *bdev_name(char *buf, char *end, struct block_device *bdev,
 }
 #endif
 
+#if !defined(CONFIG_KALLSYMS) && defined(CONFIG_MODULES)
+static int sprint_module_info(char *buf, char *end, unsigned long value,
+			     const char *fmt, int modbuildid, int backtrace, int symbol)
+{
+	struct module *mod;
+	unsigned long offset = 0;
+	unsigned long base;
+	char *modname;
+	int len;
+	const unsigned char *buildid = NULL;
+
+	if (is_ksym_addr(value))
+		return 0;
+
+	if (backtrace || symbol)
+		offset = 1;
+
+	preempt_disable();
+	mod = __module_address(value);
+	if (mod) {
+		modname = mod->name;
+#if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID)
+		if (modbuildid)
+			buildid = mod->build_id;
+#endif
+		if (offset) {
+			base = (unsigned long)mod->core_layout.base;
+			offset = value - base;
+		}
+	}
+
+	preempt_enable();
+	if (!mod)
+		return 0;
+
+	/* address belongs to module */
+	if (offset)
+		len = sprintf(buf, "0x%p+0x%lx", (void *)base, offset);
+	else
+		len = sprintf(buf, "0x%lx", (void *)value);
+
+	len += fill_name_build_id(buf, modname, modbuildid, buildid, len);
+	return len;
+}
+#else
+static inline int sprint_module_info(char *buf, char *end, unsigned long value,
+			     const char *fmt)
+{
+	return 0;
+}
+#endif
+
 static noinline_for_stack
 char *symbol_string(char *buf, char *end, void *ptr,
 		    struct printf_spec spec, const char *fmt)
 {
 	unsigned long value;
-#ifdef CONFIG_KALLSYMS
 	char sym[KSYM_SYMBOL_LEN];
-#endif
+	int backtrace = 0, symbol = 0, build_id = 0;
 
 	if (fmt[1] == 'R')
 		ptr = __builtin_extract_return_addr(ptr);
 	value = (unsigned long)ptr;
 
-#ifdef CONFIG_KALLSYMS
-	if (*fmt == 'B' && fmt[1] == 'b')
-		sprint_backtrace_build_id(sym, value);
-	else if (*fmt == 'B')
-		sprint_backtrace(sym, value);
-	else if (*fmt == 'S' && (fmt[1] == 'b' || (fmt[1] == 'R' && fmt[2] == 'b')))
-		sprint_symbol_build_id(sym, value);
-	else if (*fmt != 's')
-		sprint_symbol(sym, value);
-	else
-		sprint_symbol_no_offset(sym, value);
+	if (fmt[0] == 'B' && fmt[1] == 'b') {
+		backtrace = 1;
+		build_id = 1;
+	} else if (fmt[0] == 'B')
+		backtrace = 1;
+	else if (fmt[0] == 'S' && (fmt[1] == 'b' || (fmt[1] == 'R' && fmt[2] == 'b'))) {
+		symbol = 1;
+		build_id = 1;
+	} else if (fmt[0] != 's')
+		symbol = 1;
+	else {
+		/* Do Nothing, no offset */
+	}
 
+#ifdef CONFIG_KALLSYMS
+	sprint_kallsym_common(sym, value, build_id, backtrace, symbol);
 	return string_nocheck(buf, end, sym, spec);
 #else
+	if (sprint_module_info(sym, end, value, fmt, build_id, backtrace, symbol))
+		return string_nocheck(buf, end, sym, spec);
+
 	return special_hex_number(buf, end, value, sizeof(void *));
 #endif
 }
-- 
2.17.1

Re: [PATCH v2] kallsyms: enhance %pS/s/b printing when KALLSYSMS is disabled

[Andy Shevchenko]

On Tue, Mar 15, 2022 at 03:21:12PM +0530, Maninder Singh wrote:
> print module information when KALLSYMS is disabled.
> 
> No change for %pB, as it needs to know symbol name to adjust address
> value which can't be done without KALLSYMS.

...

> +int sprint_kallsym_common(char *buffer, unsigned long address, int build_id,
> +			    int backtrace, int symbol)
> +{
> +	if (backtrace)
> +		return __sprint_symbol(buffer, address, -1, 1, build_id);

> +	else if (symbol)
> +		return __sprint_symbol(buffer, address, 0, 1, build_id);
> +	else
> +		return __sprint_symbol(buffer, address, 0, 0, 0);

Redundant 'else' in both cases.

> +}

...

> +static int sprint_module_info(char *buf, char *end, unsigned long value,
> +			     const char *fmt, int modbuildid, int backtrace, int symbol)

fmt is not used.

> +{
> +	struct module *mod;
> +	unsigned long offset = 0;

> +	unsigned long base;

Can it be the same type as core_layout.base? Why not?

> +	char *modname;
> +	int len;
> +	const unsigned char *buildid = NULL;
> +
> +	if (is_ksym_addr(value))
> +		return 0;
> +
> +	if (backtrace || symbol)
> +		offset = 1;

I would expect here to have

	else
		offset = 0;

But see below.

> +	preempt_disable();
> +	mod = __module_address(value);
> +	if (mod) {
> +		modname = mod->name;
> +#if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID)
> +		if (modbuildid)
> +			buildid = mod->build_id;
> +#endif

> +		if (offset) {

This seems quite confusing because semantically you use offset as a boolean
flag and offset. Why not add a boolean variable with a clear name?

> +			base = (unsigned long)mod->core_layout.base;
> +			offset = value - base;
> +		}
> +	}

> +

Probably you can drop this blank line to group entire critical section,
or add a blank line above.

> +	preempt_enable();
> +	if (!mod)
> +		return 0;
> +
> +	/* address belongs to module */
> +	if (offset)
> +		len = sprintf(buf, "0x%p+0x%lx", (void *)base, offset);
> +	else

> +		len = sprintf(buf, "0x%lx", (void *)value);

What this casting is for? Don't you have a compilation warning?

> +	len += fill_name_build_id(buf, modname, modbuildid, buildid, len);
> +	return len;

	return len + ...;

?

> +}

-- 
With Best Regards,
Andy Shevchenko

RE: [PATCH v2] kallsyms: enhance %pS/s/b printing when KALLSYSMS is disabled

[Maninder Singh]

[-- Attachment #1: Type: text/plain, Size: 2473 bytes --]

Hi,

> > +int sprint_kallsym_common(char *buffer, unsigned long address, int build_id,
> > +			    int backtrace, int symbol)
> > +{
> > +	if (backtrace)
> > +		return __sprint_symbol(buffer, address, -1, 1, build_id);
> 
> > +	else if (symbol)
> > +		return __sprint_symbol(buffer, address, 0, 1, build_id);
> > +	else
> > +		return __sprint_symbol(buffer, address, 0, 0, 0);
> 
> Redundant 'else' in both cases.
>

Ok, will change it

> > +}
> 
> ...
> 
> > +static int sprint_module_info(char *buf, char *end, unsigned long value,
> > +			     const char *fmt, int modbuildid, int backtrace, int symbol)
> 
> fmt is not used.

Yes, did not notice it.(will remove both end and gmt)

> > +{
> > +	struct module *mod;
> > +	unsigned long offset = 0;
> 
> > +	unsigned long base;
> 
> Can it be the same type as core_layout.base? Why not?
>
> > +	char *modname;
> > +	int len;
> > +	const unsigned char *buildid = NULL;
> > +
> > +	if (is_ksym_addr(value))
> > +		return 0;
> > +
> > +	if (backtrace || symbol)
> > +		offset = 1;
> 
> I would expect here to have
> 
> 	else
> 		offset = 0;
> 
> But see below.
> 
> > +	preempt_disable();
> > +	mod = __module_address(value);
> > +	if (mod) {
> > +		modname = mod->name;
> > +#if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID)
> > +		if (modbuildid)
> > +			buildid = mod->build_id;
> > +#endif
> 
> > +		if (offset) {
> 
> This seems quite confusing because semantically you use offset as a boolean
> flag and offset. Why not add a boolean variable with a clear name?
>

Ok, will add 2 separate variables.

> > +			base = (unsigned long)mod->core_layout.base;
> > +			offset = value - base;
> > +		}
> > +	}
> 
> > +
> 
> Probably you can drop this blank line to group entire critical section,
> or add a blank line above.
> 
> > +	preempt_enable();
> > +	if (!mod)
> > +		return 0;
> > +
> > +	/* address belongs to module */
> > +	if (offset)
> > +		len = sprintf(buf, "0x%p+0x%lx", (void *)base, offset);
> > +	else
> 
> > +		len = sprintf(buf, "0x%lx", (void *)value);
> 
> What this casting is for? Don't you have a compilation warning?

My Bad, earlier I made patch with hashing this value also (%p), but after that
changed it to %lx to have same original behavior in case of %ps, forgot to update final patch
to remove typecast.

> 
> > +	len += fill_name_build_id(buf, modname, modbuildid, buildid, len);
> > +	return len;
> 
> 	return len + ...;
> 
> ?
> 
> > +}

Will modify patch with all changes.

Thanks,
Maninder Singh

[-- Attachment #2: rcptInfo.txt --]
[-- Type: application/octet-stream, Size: 1664 bytes --]


   =================================================================================================================================
      Subject    : Re: [PATCH v2] kallsyms: enhance %pS/s/b printing when KALLSYSMS is disabled
      From       : null
      Sent Date  : 2022-03-15 16:02  GMT+5:30
   =================================================================================================================================
                  Name                Type          Job Title                       Dept.                               Company                
   =================================================================================================================================
      Maninder Singh                 TO         Staff Engineer             System S/W Group /SRI-Delhi               Samsung Electronics 
      mcgrof@kernel.org              CC
      pmladek@suse.com               CC
      rostedt@goodmis.org            CC
      senozhatsky@chromium.org       CC
      linux@rasmusvillemoes.dk       CC
      akpm@linux-foundation.org      CC
      wangkefeng.wang@huawei.com     CC
      Vaneet Narang                  CC         Associate Architect        System S/W Group /SRI-Delhi               Samsung Electronics
      swboyd@chromium.org            CC
      ojeda@kernel.org               CC
      linux-kernel@vger.kernel.org   CC
      linux-modules@vger.kernel...   CC
      avimalin@gmail.com             CC
      atomlin@redhat.com             CC
   =================================================================================================================================