linux-kernel - [PATCH 1/5] kallsyms: Revert "Take callthunks into account"

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Message-ID: <20221028194453.330970755@infradead.org>
Date:   Fri, 28 Oct 2022 21:40:23 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        djwong@...nel.org, yujie.liu@...el.com, tglx@...utronix.de,
        jpoimboe@...nel.org, joao.moreira@...el.com,
        samitolvanen@...gle.com
Subject: [PATCH 1/5] kallsyms: Revert "Take callthunks into account"

This is a full revert of commit:

  f1389181622a ("kallsyms: Take callthunks into account")

The commit assumes a number of things that are not quite right.
Notably it assumes every symbol has PADDING_BYTES in front of it that
are not claimed by another symbol.

This is not true; even when compiled with:

  -fpatchable-function-entry=${PADDING_BYTES},${PADDING_BYTES}

Notably things like .cold subfunctions do not need to adhere to this
change in ABI. It it also not true when build with CFI_CLANG, which
claims these PADDING_BYTES in the __cfi_##name symbol.

Once the prefix bytes are not consistent and or otherwise claimed the
approach this patch takes goes out the window and kallsym resolution
will report invalid symbol names.

Therefore revert this to make room for another approach.

Reported-by: Reported-by: kernel test robot <yujie.liu@...el.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lore.kernel.org/r/202210241614.2ae4c1f5-yujie.liu@intel.com
---
 kernel/kallsyms.c |   45 +++++----------------------------------------
 1 file changed, 5 insertions(+), 40 deletions(-)

--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -293,12 +293,6 @@ static unsigned long get_symbol_pos(unsi
 	return low;
 }
 
-#ifdef CONFIG_FUNCTION_PADDING_BYTES
-#define PADDING_BYTES	CONFIG_FUNCTION_PADDING_BYTES
-#else
-#define PADDING_BYTES	0
-#endif
-
 /*
  * Lookup an address but don't bother to find any names.
  */
@@ -306,25 +300,13 @@ int kallsyms_lookup_size_offset(unsigned
 				unsigned long *offset)
 {
 	char namebuf[KSYM_NAME_LEN];
-	int ret;
-
-	addr += PADDING_BYTES;
 
 	if (is_ksym_addr(addr)) {
 		get_symbol_pos(addr, symbolsize, offset);
-		ret = 1;
-		goto found;
+		return 1;
 	}
-
-	ret = !!module_address_lookup(addr, symbolsize, offset, NULL, NULL, namebuf);
-	if (!ret) {
-		ret = !!__bpf_address_lookup(addr, symbolsize,
-					     offset, namebuf);
-	}
-found:
-	if (ret && offset)
-		*offset -= PADDING_BYTES;
-	return ret;
+	return !!module_address_lookup(addr, symbolsize, offset, NULL, NULL, namebuf) ||
+	       !!__bpf_address_lookup(addr, symbolsize, offset, namebuf);
 }
 
 static const char *kallsyms_lookup_buildid(unsigned long addr,
@@ -337,8 +319,6 @@ static const char *kallsyms_lookup_build
 	namebuf[KSYM_NAME_LEN - 1] = 0;
 	namebuf[0] = 0;
 
-	addr += PADDING_BYTES;
-
 	if (is_ksym_addr(addr)) {
 		unsigned long pos;
 
@@ -368,8 +348,6 @@ static const char *kallsyms_lookup_build
 
 found:
 	cleanup_symbol_name(namebuf);
-	if (ret && offset)
-		*offset -= PADDING_BYTES;
 	return ret;
 }
 
@@ -396,8 +374,6 @@ int lookup_symbol_name(unsigned long add
 	symname[0] = '\0';
 	symname[KSYM_NAME_LEN - 1] = '\0';
 
-	addr += PADDING_BYTES;
-
 	if (is_ksym_addr(addr)) {
 		unsigned long pos;
 
@@ -425,8 +401,6 @@ int lookup_symbol_attrs(unsigned long ad
 	name[0] = '\0';
 	name[KSYM_NAME_LEN - 1] = '\0';
 
-	addr += PADDING_BYTES;
-
 	if (is_ksym_addr(addr)) {
 		unsigned long pos;
 
@@ -443,8 +417,6 @@ int lookup_symbol_attrs(unsigned long ad
 		return res;
 
 found:
-	if (offset)
-		*offset -= PADDING_BYTES;
 	cleanup_symbol_name(name);
 	return 0;
 }
@@ -470,15 +442,8 @@ static int __sprint_symbol(char *buffer,
 	len = strlen(buffer);
 	offset -= symbol_offset;
 
-	if (add_offset) {
-		char s = '+';
-
-		if ((long)offset < 0) {
-			s = '-';
-			offset = 0UL - offset;
-		}
-		len += sprintf(buffer + len, "%c%#lx/%#lx", s, offset, size);
-	}
+	if (add_offset)
+		len += sprintf(buffer + len, "+%#lx/%#lx", offset, size);
 
 	if (modname) {
 		len += sprintf(buffer + len, " [%s", modname);