Draft: Fix dynrela func pointers on x86 and ppc64le

kpatch-build/create-diff-object.c

@@ -3240,19 +3240,35 @@ static bool is_expoline(struct kpatch_elf *kelf, char *name)
 static int function_ptr_rela(const struct rela *rela, struct kpatch_elf *kelf)
 {
 	const struct rela *rela_toc = toc_rela(rela);
+	static int entry_offset = -1;
 	bool funcptr = false;
 
+	if (entry_offset < 0) {
+		char *str = getenv("ENTRY_OFFSET_BYTES");
+		if (str)
+			entry_offset = atoi(str);
+		else
+			entry_offset = 0;
+	}
+
 	if (rela_toc && rela_toc->sym->type == STT_FUNC && !rela_toc->sym->parent) {
 		switch (kelf->arch) {
 		case X86_64:
-			if (rela_toc->addend == (int)rela_toc->sym->sym.st_value &&
+			if (rela_toc->addend + entry_offset == (int)rela_toc->sym->sym.st_value &&
 			    rela->type == R_X86_64_32S)
 				funcptr = true;
 			break;
 		case PPC64:
-			if (rela_toc->addend == (int)rela_toc->sym->sym.st_value &&
-			    (rela->type == R_PPC64_TOC16_HA || rela->type == R_PPC64_TOC16_LO_DS))
+			if ((rela->type == R_PPC64_TOC16_HA || rela->type == R_PPC64_TOC16_LO_DS) &&
+			    (rela_toc->addend == (int)rela_toc->sym->sym.st_value)) {
 				funcptr = true;
+			} else if (rela->type == R_PPC64_ADDR64) {
+				struct rela *entry;
+				entry = find_rela_by_offset(rela_toc->sym->sec->rela,
+							    (unsigned int) (rela_toc->addend + rela_toc->sym->sym.st_value));
+				if (entry && entry->type == R_PPC64_ENTRY)
+					funcptr = true;
+			}
 			break;
 		case S390:
 			if (rela->type == R_390_GOTENT)

kpatch-build/kpatch-build

@@ -472,6 +472,31 @@ find_special_section_data() {
 	return
 }
 
+# Determine if this configuration uses the -fpatchable-function-entry=N[,M]
+# compiler flag, for which create-diff-object will need to know any non-zero M
+# NOPs value (i.e. to expect an entry point M NOPs instructions inside its
+# function section.)
+find_entry_offset() {
+	local entry_offset=0
+
+	case "$ARCH" in
+		"x86_64")
+			# arch/x86/Makefile: For CONFIG_CALL_PADDING, sets M=CONFIG_FUNCTION_PADDING_BYTES
+			if [[ -n "$CONFIG_CALL_PADDING" ]]; then
+				entry_offset="$CONFIG_FUNCTION_PADDING_BYTES"
+			fi
+			;;
+		"ppc64le")
+			# arch/powerpc/Makefile: N/A
+			;;
+		"s390x")
+			# arch/s390x/Makefile: N/A
+			;;
+	esac
+
+	export ENTRY_OFFSET_BYTES="$entry_offset"
+}
+
 # path of file, relative to dir
 # adapted from https://stackoverflow.com/a/24848739
 relpath() {
@@ -1262,6 +1287,7 @@ export KCFLAGS="-I$DATADIR/patch -ffunction-sections -fdata-sections \
 
 echo "Reading special section data"
 find_special_section_data
+find_entry_offset
 
 if [[ $DEBUG -ge 4 ]]; then
 	export KPATCH_GCC_DEBUG=1

test/integration/rhel-7.9/func-ptr-klp_reloc.patch

@@ -0,0 +1,17 @@
+--- src.old/fs/proc/uptime.c	2024-06-13 03:19:08.000000000 -0400
++++ src/fs/proc/uptime.c	2025-03-25 09:08:38.206910364 -0400
+@@ -24,11 +24,12 @@ static int uptime_proc_show(struct seq_f
+ 	nsec = cputime64_to_jiffies64(idletime) * TICK_NSEC;
+ 	idle.tv_sec = div_u64_rem(nsec, NSEC_PER_SEC, &rem);
+ 	idle.tv_nsec = rem;
+-	seq_printf(m, "%lu.%02lu %lu.%02lu\n",
++	seq_printf(m, "%lu.%02lu %lu.%02lu uptime_proc_show=%p\n",
+ 			(unsigned long) uptime.tv_sec,
+ 			(uptime.tv_nsec / (NSEC_PER_SEC / 100)),
+ 			(unsigned long) idle.tv_sec,
+-			(idle.tv_nsec / (NSEC_PER_SEC / 100)));
++			(idle.tv_nsec / (NSEC_PER_SEC / 100)),
++			uptime_proc_show);
+ 	return 0;
+ }
+

test/integration/rhel-7.9/func-ptr-klp_reloc.test

@@ -0,0 +1,9 @@
+#!/bin/bash
+
+kpatch_value=$(cat /proc/uptime | grep -o 'uptime_proc_show=.*' | awk -F= '{print $2}')
+kernel_value=$(awk '$NF=="uptime_proc_show" { print $1 }' /proc/kallsyms)
+
+if [[ "$kpatch_value" != "$kernel_value" ]]; then
+        echo "kpatch_value($kpatch_value) != kernel_value($kernel_value)"
+        exit 1
+fi

test/integration/rhel-8.10/func-ptr-klp_reloc.patch

@@ -0,0 +1,17 @@
+--- src.old/fs/proc/uptime.c	2025-03-20 06:57:19.000000000 -0400
++++ src/fs/proc/uptime.c	2025-03-25 09:35:50.847697946 -0400
+@@ -25,11 +25,12 @@ static int uptime_proc_show(struct seq_f
+
+ 	idle.tv_sec = div_u64_rem(nsec, NSEC_PER_SEC, &rem);
+ 	idle.tv_nsec = rem;
+-	seq_printf(m, "%lu.%02lu %lu.%02lu\n",
++	seq_printf(m, "%lu.%02lu %lu.%02lu uptime_proc_show=%pK\n",
+ 			(unsigned long) uptime.tv_sec,
+ 			(uptime.tv_nsec / (NSEC_PER_SEC / 100)),
+ 			(unsigned long) idle.tv_sec,
+-			(idle.tv_nsec / (NSEC_PER_SEC / 100)));
++			(idle.tv_nsec / (NSEC_PER_SEC / 100)),
++			uptime_proc_show);
+ 	return 0;
+ }
+

test/integration/rhel-8.10/func-ptr-klp_reloc.test

@@ -0,0 +1,9 @@
+#!/bin/bash
+
+kpatch_value=$(cat /proc/uptime | grep -o 'uptime_proc_show=.*' | awk -F= '{print $2}')
+kernel_value=$(awk '$NF=="uptime_proc_show" { print $1 }' /proc/kallsyms)
+
+if [[ "$kpatch_value" != "$kernel_value" ]]; then
+        echo "kpatch_value($kpatch_value) != kernel_value($kernel_value)"
+        exit 1
+fi

test/integration/rhel-9.5/func-ptr-klp_reloc.patch

@@ -0,0 +1,17 @@
+--- src.old/fs/proc/uptime.c	2025-03-25 09:35:31.468574086 -0400
++++ src/fs/proc/uptime.c	2025-03-25 09:35:46.848570153 -0400
+@@ -29,11 +29,12 @@ static int uptime_proc_show(struct seq_f
+
+ 	idle.tv_sec = div_u64_rem(idle_nsec, NSEC_PER_SEC, &rem);
+ 	idle.tv_nsec = rem;
+-	seq_printf(m, "%lu.%02lu %lu.%02lu\n",
++	seq_printf(m, "%lu.%02lu %lu.%02lu uptime_proc_show=%pK\n",
+ 			(unsigned long) uptime.tv_sec,
+ 			(uptime.tv_nsec / (NSEC_PER_SEC / 100)),
+ 			(unsigned long) idle.tv_sec,
+-			(idle.tv_nsec / (NSEC_PER_SEC / 100)));
++			(idle.tv_nsec / (NSEC_PER_SEC / 100)),
++			uptime_proc_show);
+ 	return 0;
+ }
+

test/integration/rhel-9.5/func-ptr-klp_reloc.test

@@ -0,0 +1,9 @@
+#!/bin/bash
+
+kpatch_value=$(cat /proc/uptime | grep -o 'uptime_proc_show=.*' | awk -F= '{print $2}')
+kernel_value=$(awk '$NF=="uptime_proc_show" { print $1 }' /proc/kallsyms)
+
+if [[ "$kpatch_value" != "$kernel_value" ]]; then
+        echo "kpatch_value($kpatch_value) != kernel_value($kernel_value)"
+        exit 1
+fi