* [PATCH v2 1/6] s390/tools: Pass symbol name to do_relocs()
2026-07-27 14:05 [PATCH v2 0/6] s390: Add kCFI support Heiko Carstens
@ 2026-07-27 14:05 ` Heiko Carstens
2026-07-27 14:05 ` [PATCH v2 2/6] s390/tools/relocs: Ignore __kcfi_typeid_ relocations Heiko Carstens
` (4 subsequent siblings)
5 siblings, 0 replies; 8+ messages in thread
From: Heiko Carstens @ 2026-07-27 14:05 UTC (permalink / raw)
To: Stefan Schulze Frielinghaus, Juergen Christ, Ilya Leoshkevich,
Dominik Steenken, Alexander Gordeev, Sven Schnelle, Vasily Gorbik,
Christian Borntraeger, Maxim Khmelevskii, Jens Remus,
Sami Tolvanen, Kees Cook, Nathan Chancellor, Alexei Starovoitov,
Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman,
Kumar Kartikeya Dwivedi
Cc: llvm, bpf, linux-s390, linux-kernel
Pass the symbol symbol name which corresponds to a relocation to
do_relocs(). This is preparation for kCFI support.
Given that the s390 specific relocs tool is a stripped down version of the
x86 version, add more code from the x86 version to the s390 version, while
keeping coding style, etc. in order to add the required functionality.
Reviewed-by: Jens Remus <jremus@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
---
arch/s390/tools/relocs.c | 142 ++++++++++++++++++++++++++++++++++++++-
1 file changed, 139 insertions(+), 3 deletions(-)
diff --git a/arch/s390/tools/relocs.c b/arch/s390/tools/relocs.c
index 30a732c808f3..a2774176d38f 100644
--- a/arch/s390/tools/relocs.c
+++ b/arch/s390/tools/relocs.c
@@ -41,6 +41,10 @@
static Elf_Ehdr ehdr;
static unsigned long shnum;
static unsigned int shstrndx;
+static unsigned int shsymtabndx;
+static unsigned int shxsymtabndx;
+
+static int sym_index(Elf_Sym *sym);
struct relocs {
uint32_t *offset;
@@ -54,11 +58,40 @@ static struct relocs relocs64;
struct section {
Elf_Shdr shdr;
struct section *link;
+ Elf_Sym *symtab;
+ Elf32_Word *xsymtab;
Elf_Rel *reltab;
+ char *strtab;
};
static struct section *secs;
+static const char *sec_name(unsigned shndx)
+{
+ const char *sec_strtab;
+ const char *name = "<noname>";
+ sec_strtab = secs[shstrndx].strtab;
+
+ if (shndx < shnum)
+ name = sec_strtab + secs[shndx].shdr.sh_name;
+ else if (shndx == SHN_ABS)
+ name = "ABSOLUTE";
+ else if (shndx == SHN_COMMON)
+ name = "COMMON";
+ return name;
+}
+
+static const char *sym_name(const char *sym_strtab, Elf_Sym *sym)
+{
+ const char *name;
+
+ if (sym->st_name)
+ name = sym_strtab + sym->st_name;
+ else
+ name = sec_name(sym_index(sym));
+ return name;
+}
+
#if BYTE_ORDER == LITTLE_ENDIAN
#define le16_to_cpu(val) (val)
#define le32_to_cpu(val) (val)
@@ -105,6 +138,23 @@ static uint64_t elf64_to_cpu(uint64_t val)
#define elf_off_to_cpu(x) elf64_to_cpu(x)
#define elf_xword_to_cpu(x) elf64_to_cpu(x)
+static int sym_index(Elf_Sym *sym)
+{
+ Elf_Sym *symtab = secs[shsymtabndx].symtab;
+ Elf32_Word *xsymtab = secs[shxsymtabndx].xsymtab;
+ unsigned long offset;
+ int index;
+
+ if (sym->st_shndx != SHN_XINDEX)
+ return sym->st_shndx;
+
+ /* calculate offset of sym from head of table. */
+ offset = (unsigned long)sym - (unsigned long)symtab;
+ index = offset / sizeof(*sym);
+
+ return elf32_to_cpu(xsymtab[index]);
+}
+
static void die(char *fmt, ...)
{
va_list ap;
@@ -216,6 +266,81 @@ static void read_shdrs(FILE *fp)
}
+static void read_strtabs(FILE *fp)
+{
+ int i;
+
+ for (i = 0; i < shnum; i++) {
+ struct section *sec = &secs[i];
+
+ if (sec->shdr.sh_type != SHT_STRTAB)
+ continue;
+
+ sec->strtab = malloc(sec->shdr.sh_size);
+ if (!sec->strtab)
+ die("malloc of %" FMT " bytes for strtab failed\n", sec->shdr.sh_size);
+
+ if (fseek(fp, sec->shdr.sh_offset, SEEK_SET) < 0)
+ die("Seek to %" FMT " failed: %s\n", sec->shdr.sh_offset, strerror(errno));
+
+ if (fread(sec->strtab, 1, sec->shdr.sh_size, fp) != sec->shdr.sh_size)
+ die("Cannot read symbol table: %s\n", strerror(errno));
+ }
+}
+
+static void read_symtabs(FILE *fp)
+{
+ int i, j;
+
+ for (i = 0; i < shnum; i++) {
+ struct section *sec = &secs[i];
+ int num_syms;
+
+ switch (sec->shdr.sh_type) {
+ case SHT_SYMTAB_SHNDX:
+ sec->xsymtab = malloc(sec->shdr.sh_size);
+ if (!sec->xsymtab)
+ die("malloc of %" FMT " bytes for xsymtab failed\n", sec->shdr.sh_size);
+
+ if (fseek(fp, sec->shdr.sh_offset, SEEK_SET) < 0)
+ die("Seek to %" FMT " failed: %s\n", sec->shdr.sh_offset, strerror(errno));
+
+ if (fread(sec->xsymtab, 1, sec->shdr.sh_size, fp) != sec->shdr.sh_size)
+ die("Cannot read extended symbol table: %s\n", strerror(errno));
+
+ shxsymtabndx = i;
+ continue;
+
+ case SHT_SYMTAB:
+ num_syms = sec->shdr.sh_size / sizeof(Elf_Sym);
+
+ sec->symtab = malloc(sec->shdr.sh_size);
+ if (!sec->symtab)
+ die("malloc of %" FMT " bytes for symtab failed\n", sec->shdr.sh_size);
+
+ if (fseek(fp, sec->shdr.sh_offset, SEEK_SET) < 0)
+ die("Seek to %" FMT " failed: %s\n", sec->shdr.sh_offset, strerror(errno));
+
+ if (fread(sec->symtab, 1, sec->shdr.sh_size, fp) != sec->shdr.sh_size)
+ die("Cannot read symbol table: %s\n", strerror(errno));
+
+ for (j = 0; j < num_syms; j++) {
+ Elf_Sym *sym = &sec->symtab[j];
+
+ sym->st_name = elf_word_to_cpu(sym->st_name);
+ sym->st_value = elf_addr_to_cpu(sym->st_value);
+ sym->st_size = elf_xword_to_cpu(sym->st_size);
+ sym->st_shndx = elf_half_to_cpu(sym->st_shndx);
+ }
+ shsymtabndx = i;
+ continue;
+
+ default:
+ continue;
+ }
+ }
+}
+
static void read_relocs(FILE *fp)
{
int i, j;
@@ -263,7 +388,8 @@ static void add_reloc(struct relocs *r, uint32_t offset)
r->offset[r->count++] = offset;
}
-static int do_reloc(struct section *sec, Elf_Rel *rel)
+static int do_reloc(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym,
+ const char *symname)
{
unsigned int r_type = ELF64_R_TYPE(rel->r_info);
ElfW(Addr) offset = rel->r_offset;
@@ -296,21 +422,29 @@ static void walk_relocs(void)
/* Walk through the relocations */
for (i = 0; i < shnum; i++) {
- struct section *sec_applies;
+ char *sym_strtab;
+ Elf_Sym *sh_symtab;
+ struct section *sec_applies, *sec_symtab;
int j;
struct section *sec = &secs[i];
if (sec->shdr.sh_type != SHT_REL_TYPE)
continue;
+ sec_symtab = sec->link;
sec_applies = &secs[sec->shdr.sh_info];
if (!(sec_applies->shdr.sh_flags & SHF_ALLOC))
continue;
+ sh_symtab = sec_symtab->symtab;
+ sym_strtab = sec_symtab->link->strtab;
+
for (j = 0; j < sec->shdr.sh_size / sizeof(Elf_Rel); j++) {
Elf_Rel *rel = &sec->reltab[j];
+ Elf_Sym *sym = &sh_symtab[ELF_R_SYM(rel->r_info)];
+ const char *symname = sym_name(sym_strtab, sym);
- do_reloc(sec, rel);
+ do_reloc(sec, rel, sym, symname);
}
}
}
@@ -349,6 +483,8 @@ static void process(FILE *fp)
{
read_ehdr(fp);
read_shdrs(fp);
+ read_strtabs(fp);
+ read_symtabs(fp);
read_relocs(fp);
emit_relocs();
}
--
2.53.0
^ permalink raw reply related [flat|nested] 8+ messages in thread* [PATCH v2 2/6] s390/tools/relocs: Ignore __kcfi_typeid_ relocations
2026-07-27 14:05 [PATCH v2 0/6] s390: Add kCFI support Heiko Carstens
2026-07-27 14:05 ` [PATCH v2 1/6] s390/tools: Pass symbol name to do_relocs() Heiko Carstens
@ 2026-07-27 14:05 ` Heiko Carstens
2026-07-27 14:05 ` [PATCH v2 3/6] s390: Add ftrace_stub_graph Heiko Carstens
` (3 subsequent siblings)
5 siblings, 0 replies; 8+ messages in thread
From: Heiko Carstens @ 2026-07-27 14:05 UTC (permalink / raw)
To: Stefan Schulze Frielinghaus, Juergen Christ, Ilya Leoshkevich,
Dominik Steenken, Alexander Gordeev, Sven Schnelle, Vasily Gorbik,
Christian Borntraeger, Maxim Khmelevskii, Jens Remus,
Sami Tolvanen, Kees Cook, Nathan Chancellor, Alexei Starovoitov,
Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman,
Kumar Kartikeya Dwivedi
Cc: llvm, bpf, linux-s390, linux-kernel
This is the s390 variant of commit ca7e10bff196 ("x86/tools/relocs: Ignore
__kcfi_typeid_ relocations"):
"The compiler generates __kcfi_typeid_ symbols for annotating assembly
functions with type information. These are constants that can be referenced
in assembly code and are resolved by the linker. Ignore them in relocs."
Reviewed-by: Jens Remus <jremus@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
---
arch/s390/tools/relocs.c | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
diff --git a/arch/s390/tools/relocs.c b/arch/s390/tools/relocs.c
index a2774176d38f..72178dc90a4c 100644
--- a/arch/s390/tools/relocs.c
+++ b/arch/s390/tools/relocs.c
@@ -405,6 +405,22 @@ static int do_reloc(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym,
case R_390_GOTPCDBL:
case R_390_GOTOFF64:
break;
+ case R_390_32: {
+ static const char kcfipfx[] = "__kcfi_typeid_";
+
+ if (sym->st_shndx != SHN_ABS)
+ die("Unsupported relocation type: %d\n", r_type);
+ /*
+ * Symbols with __kcfi_typeid_ prefix have constant values,
+ * which do not change if bzImage is loaded at a different
+ * physical address than the address for which it has been
+ * compiled.
+ */
+ if (!strncmp(kcfipfx, symname, sizeof(kcfipfx) - 1))
+ break;
+ die("Invalid absolute R_390_32 relocation: %s\n", symname);
+ break;
+ }
case R_390_64:
add_reloc(&relocs64, offset);
break;
--
2.53.0
^ permalink raw reply related [flat|nested] 8+ messages in thread* [PATCH v2 3/6] s390: Add ftrace_stub_graph
2026-07-27 14:05 [PATCH v2 0/6] s390: Add kCFI support Heiko Carstens
2026-07-27 14:05 ` [PATCH v2 1/6] s390/tools: Pass symbol name to do_relocs() Heiko Carstens
2026-07-27 14:05 ` [PATCH v2 2/6] s390/tools/relocs: Ignore __kcfi_typeid_ relocations Heiko Carstens
@ 2026-07-27 14:05 ` Heiko Carstens
2026-07-27 14:05 ` [PATCH v2 4/6] s390/diag: Generate CFI type information for assembly functions Heiko Carstens
` (2 subsequent siblings)
5 siblings, 0 replies; 8+ messages in thread
From: Heiko Carstens @ 2026-07-27 14:05 UTC (permalink / raw)
To: Stefan Schulze Frielinghaus, Juergen Christ, Ilya Leoshkevich,
Dominik Steenken, Alexander Gordeev, Sven Schnelle, Vasily Gorbik,
Christian Borntraeger, Maxim Khmelevskii, Jens Remus,
Sami Tolvanen, Kees Cook, Nathan Chancellor, Alexei Starovoitov,
Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman,
Kumar Kartikeya Dwivedi
Cc: llvm, bpf, linux-s390, linux-kernel
This is the s390 variant of commit f3a0c23f2539 ("riscv: Add
ftrace_stub_graph"):
"Commit 883bbbffa5a4 ("ftrace,kcfi: Separate ftrace_stub() and
ftrace_stub_graph()") added a separate ftrace_stub_graph function for
CFI_CLANG. Add the stub to fix FUNCTION_GRAPH_TRACER compatibility
with CFI."
Reviewed-by: Jens Remus <jremus@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
---
arch/s390/kernel/mcount.S | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/arch/s390/kernel/mcount.S b/arch/s390/kernel/mcount.S
index 1fec370fecf4..6bc44c767642 100644
--- a/arch/s390/kernel/mcount.S
+++ b/arch/s390/kernel/mcount.S
@@ -4,6 +4,7 @@
*
*/
+#include <linux/cfi_types.h>
#include <linux/linkage.h>
#include <asm/asm-offsets.h>
#include <asm/ftrace.h>
@@ -34,10 +35,16 @@
.section .kprobes.text, "ax"
-SYM_FUNC_START(ftrace_stub)
+SYM_TYPED_FUNC_START(ftrace_stub)
BR_EX %r14
SYM_FUNC_END(ftrace_stub)
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+SYM_TYPED_FUNC_START(ftrace_stub_graph)
+ BR_EX %r14
+SYM_FUNC_END(ftrace_stub_graph)
+#endif
+
SYM_CODE_START(ftrace_stub_direct_tramp)
lgr %r1, %r0
BR_EX %r1
--
2.53.0
^ permalink raw reply related [flat|nested] 8+ messages in thread* [PATCH v2 4/6] s390/diag: Generate CFI type information for assembly functions
2026-07-27 14:05 [PATCH v2 0/6] s390: Add kCFI support Heiko Carstens
` (2 preceding siblings ...)
2026-07-27 14:05 ` [PATCH v2 3/6] s390: Add ftrace_stub_graph Heiko Carstens
@ 2026-07-27 14:05 ` Heiko Carstens
2026-07-27 14:05 ` [PATCH v2 5/6] s390/bpf: Add kCFI support Heiko Carstens
2026-07-27 14:05 ` [PATCH v2 6/6] s390/Kconfig: Select ARCH_SUPPORTS_CFI Heiko Carstens
5 siblings, 0 replies; 8+ messages in thread
From: Heiko Carstens @ 2026-07-27 14:05 UTC (permalink / raw)
To: Stefan Schulze Frielinghaus, Juergen Christ, Ilya Leoshkevich,
Dominik Steenken, Alexander Gordeev, Sven Schnelle, Vasily Gorbik,
Christian Borntraeger, Maxim Khmelevskii, Jens Remus,
Sami Tolvanen, Kees Cook, Nathan Chancellor, Alexei Starovoitov,
Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman,
Kumar Kartikeya Dwivedi
Cc: llvm, bpf, linux-s390, linux-kernel
Use SYM_TYPED_FUNC_START to generate __kcfi_typeid_ symbols for assembler
functions which are called indirectly. All assembler functions contained in
text_amode31.S are called indirectly and require such annotations.
Reviewed-by: Jens Remus <jremus@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
---
arch/s390/kernel/text_amode31.S | 13 +++++++------
1 file changed, 7 insertions(+), 6 deletions(-)
diff --git a/arch/s390/kernel/text_amode31.S b/arch/s390/kernel/text_amode31.S
index 26f2981aa09e..f007d892d0c5 100644
--- a/arch/s390/kernel/text_amode31.S
+++ b/arch/s390/kernel/text_amode31.S
@@ -5,6 +5,7 @@
* Copyright IBM Corp. 2019
*/
+#include <linux/cfi_types.h>
#include <linux/linkage.h>
#include <asm/asm-extable.h>
#include <asm/errno.h>
@@ -26,7 +27,7 @@
/*
* int _diag14_amode31(unsigned long rx, unsigned long ry1, unsigned long subcode)
*/
-SYM_FUNC_START(_diag14_amode31)
+SYM_TYPED_FUNC_START(_diag14_amode31)
lgr %r1,%r2
lgr %r2,%r3
lgr %r3,%r4
@@ -46,7 +47,7 @@ SYM_FUNC_END(_diag14_amode31)
/*
* int _diag210_amode31(struct diag210 *addr)
*/
-SYM_FUNC_START(_diag210_amode31)
+SYM_TYPED_FUNC_START(_diag210_amode31)
lgr %r1,%r2
lhi %r2,-1
sam31
@@ -64,7 +65,7 @@ SYM_FUNC_END(_diag210_amode31)
/*
* int diag8c(struct diag8c *addr, struct ccw_dev_id *devno, size_t len)
*/
-SYM_FUNC_START(_diag8c_amode31)
+SYM_TYPED_FUNC_START(_diag8c_amode31)
llgf %r3,0(%r3)
sam31
diag %r2,%r4,0x8c
@@ -77,7 +78,7 @@ SYM_FUNC_END(_diag8c_amode31)
/*
* int _diag26c_amode31(void *req, void *resp, enum diag26c_sc subcode)
*/
-SYM_FUNC_START(_diag26c_amode31)
+SYM_TYPED_FUNC_START(_diag26c_amode31)
lghi %r5,-EOPNOTSUPP
sam31
diag %r2,%r4,0x26c
@@ -91,7 +92,7 @@ SYM_FUNC_END(_diag26c_amode31)
/*
* void _diag0c_amode31(unsigned long rx)
*/
-SYM_FUNC_START(_diag0c_amode31)
+SYM_TYPED_FUNC_START(_diag0c_amode31)
sam31
diag %r2,%r2,0x0c
sam64
@@ -103,7 +104,7 @@ SYM_FUNC_END(_diag0c_amode31)
*
* Calls diag 308 subcode 1 and continues execution
*/
-SYM_FUNC_START(_diag308_reset_amode31)
+SYM_TYPED_FUNC_START(_diag308_reset_amode31)
larl %r4,ctlregs # Save control registers
stctg %c0,%c15,0(%r4)
lg %r2,0(%r4) # Disable lowcore protection
--
2.53.0
^ permalink raw reply related [flat|nested] 8+ messages in thread* [PATCH v2 5/6] s390/bpf: Add kCFI support
2026-07-27 14:05 [PATCH v2 0/6] s390: Add kCFI support Heiko Carstens
` (3 preceding siblings ...)
2026-07-27 14:05 ` [PATCH v2 4/6] s390/diag: Generate CFI type information for assembly functions Heiko Carstens
@ 2026-07-27 14:05 ` Heiko Carstens
2026-07-27 15:37 ` Ilya Leoshkevich
2026-07-27 14:05 ` [PATCH v2 6/6] s390/Kconfig: Select ARCH_SUPPORTS_CFI Heiko Carstens
5 siblings, 1 reply; 8+ messages in thread
From: Heiko Carstens @ 2026-07-27 14:05 UTC (permalink / raw)
To: Stefan Schulze Frielinghaus, Juergen Christ, Ilya Leoshkevich,
Dominik Steenken, Alexander Gordeev, Sven Schnelle, Vasily Gorbik,
Christian Borntraeger, Maxim Khmelevskii, Jens Remus,
Sami Tolvanen, Kees Cook, Nathan Chancellor, Alexei Starovoitov,
Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman,
Kumar Kartikeya Dwivedi
Cc: llvm, bpf, linux-s390, linux-kernel
This is the s390 variant of commit 710618c760c0 ("arm64/cfi,bpf: Support
kCFI + BPF on arm64").
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
---
arch/s390/include/asm/cfi.h | 7 +++++++
arch/s390/net/bpf_jit_comp.c | 28 ++++++++++++++++++++++++----
2 files changed, 31 insertions(+), 4 deletions(-)
create mode 100644 arch/s390/include/asm/cfi.h
diff --git a/arch/s390/include/asm/cfi.h b/arch/s390/include/asm/cfi.h
new file mode 100644
index 000000000000..9af2c7cb70ca
--- /dev/null
+++ b/arch/s390/include/asm/cfi.h
@@ -0,0 +1,7 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_S390_CFI_H
+#define _ASM_S390_CFI_H
+
+#define __bpfcall
+
+#endif /* _ASM_S390_CFI_H */
diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
index 31749c0362ca..7f45c106444d 100644
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -21,6 +21,7 @@
#include <linux/filter.h>
#include <linux/init.h>
#include <linux/bpf.h>
+#include <linux/cfi.h>
#include <linux/mm.h>
#include <linux/kernel.h>
#include <asm/cacheflush.h>
@@ -356,6 +357,19 @@ static void emit6_pcrel_rilc(struct bpf_jit *jit, u32 op, u8 mask, s64 pcrel)
} \
})
+static inline void emit_u32_data(const u32 data, struct bpf_jit *jit)
+{
+ if (jit->prg_buf)
+ *(u32 *)(jit->prg_buf + jit->prg) = data;
+ jit->prg += 4;
+}
+
+static inline void emit_kcfi(u32 hash, struct bpf_jit *jit)
+{
+ if (IS_ENABLED(CONFIG_CFI))
+ emit_u32_data(hash, jit);
+}
+
/*
* Return whether this is the first pass. The first pass is special, since we
* don't know any sizes yet, and thus must be conservative.
@@ -597,6 +611,8 @@ static void bpf_jit_prologue(struct bpf_jit *jit, struct bpf_prog *fp)
{
BUILD_BUG_ON(sizeof(struct prog_frame) != STACK_FRAME_OVERHEAD);
+ emit_kcfi(bpf_is_subprog(fp) ? cfi_bpf_subprog_hash : cfi_bpf_hash, jit);
+
/* No-op for hotpatching */
/* brcl 0,prologue_plt */
EMIT6_PCREL_RILC(0xc0040000, 0, jit->prologue_plt);
@@ -616,7 +632,7 @@ static void bpf_jit_prologue(struct bpf_jit *jit, struct bpf_prog *fp)
bpf_skip(jit, 6);
}
/* Tail calls have to skip above initialization */
- jit->tail_call_start = jit->prg;
+ jit->tail_call_start = jit->prg - cfi_get_offset();
if (fp->aux->exception_cb) {
/*
* Switch stack, the new address is in the 2nd parameter.
@@ -2401,11 +2417,13 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_verifier_env *env, struct bpf_pr
jit_data->ctx = jit;
jit_data->pass = pass;
}
- fp->bpf_func = (void *) jit.prg_buf;
+ fp->bpf_func = (void *)jit.prg_buf + cfi_get_offset();
fp->jited = 1;
- fp->jited_len = jit.size;
+ fp->jited_len = jit.size - cfi_get_offset();
if (!fp->is_func || extra_pass) {
+ for (int i = 0; i < fp->len; i++)
+ jit.addrs[i] -= cfi_get_offset();
bpf_prog_fill_jited_linfo(fp, jit.addrs + 1);
free_addrs:
kvfree(jit.addrs);
@@ -2671,8 +2689,10 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
return -ENOTSUPP;
/* Return to %r14 in the struct_ops case. */
- if (flags & BPF_TRAMP_F_INDIRECT)
+ if (flags & BPF_TRAMP_F_INDIRECT) {
flags |= BPF_TRAMP_F_SKIP_FRAME;
+ emit_kcfi(cfi_get_func_hash(func_addr), jit);
+ }
/*
* Compute how many arguments we need to pass to BPF programs.
--
2.53.0
^ permalink raw reply related [flat|nested] 8+ messages in thread* Re: [PATCH v2 5/6] s390/bpf: Add kCFI support
2026-07-27 14:05 ` [PATCH v2 5/6] s390/bpf: Add kCFI support Heiko Carstens
@ 2026-07-27 15:37 ` Ilya Leoshkevich
0 siblings, 0 replies; 8+ messages in thread
From: Ilya Leoshkevich @ 2026-07-27 15:37 UTC (permalink / raw)
To: Heiko Carstens
Cc: Stefan Schulze Frielinghaus, Juergen Christ, Dominik Steenken,
Alexander Gordeev, Sven Schnelle, Vasily Gorbik,
Christian Borntraeger, Maxim Khmelevskii, Jens Remus,
Sami Tolvanen, Kees Cook, Nathan Chancellor, Alexei Starovoitov,
Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman,
Kumar Kartikeya Dwivedi, llvm, bpf, linux-s390, linux-kernel
On 2026-07-27 16:05, Heiko Carstens wrote:
> This is the s390 variant of commit 710618c760c0 ("arm64/cfi,bpf:
> Support
> kCFI + BPF on arm64").
>
> Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
> ---
> arch/s390/include/asm/cfi.h | 7 +++++++
> arch/s390/net/bpf_jit_comp.c | 28 ++++++++++++++++++++++++----
> 2 files changed, 31 insertions(+), 4 deletions(-)
> create mode 100644 arch/s390/include/asm/cfi.h
Reviewed-by: Ilya Leoshkevich <iii@linux.ibm.com>
^ permalink raw reply [flat|nested] 8+ messages in thread
* [PATCH v2 6/6] s390/Kconfig: Select ARCH_SUPPORTS_CFI
2026-07-27 14:05 [PATCH v2 0/6] s390: Add kCFI support Heiko Carstens
` (4 preceding siblings ...)
2026-07-27 14:05 ` [PATCH v2 5/6] s390/bpf: Add kCFI support Heiko Carstens
@ 2026-07-27 14:05 ` Heiko Carstens
5 siblings, 0 replies; 8+ messages in thread
From: Heiko Carstens @ 2026-07-27 14:05 UTC (permalink / raw)
To: Stefan Schulze Frielinghaus, Juergen Christ, Ilya Leoshkevich,
Dominik Steenken, Alexander Gordeev, Sven Schnelle, Vasily Gorbik,
Christian Borntraeger, Maxim Khmelevskii, Jens Remus,
Sami Tolvanen, Kees Cook, Nathan Chancellor, Alexei Starovoitov,
Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman,
Kumar Kartikeya Dwivedi
Cc: llvm, bpf, linux-s390, linux-kernel
With all prerequisites in place select ARCH_SUPPORTS_CFI.
Note that this support is supposed to work with the generic kCFI support
which is provided by clang. This comes with a couple of limitations:
The generic kCFI implementation does not generate a .kcfi_traps section,
nor is a special instruction used in case a checksum mismatch is detected.
This means in case of checksum mismatch the kernel just crashes. It should
be quite easy to tell by the surrounding code that a crash happened because
of a checksum mismatch.
If clang and/or gcc provide a .kcfi_traps section it will be possible to
print proper CFI messages instead of just crashing the kernel (enable
ARCH_USES_CFI_TRAPS).
In addition this also means that CFI_PERMISSIVE does not work. Even if the
option is selected the kernel will crash in case of checksum mismatch.
However it seems to be acceptable to enable kCFI support to the kernel now
even if it is not perfect. Later clang and gcc extensions are required to
improve this.
As of now a crash caused by a CFI failure looks like this:
illegal operation: 0001 ilc:1 [#1]SMP
Modules linked in: bpf_testmod(OE)
CPU: 0 UID: 0 PID: 92 Comm: test_progs Tainted: G OE 7.2.0-rc4-00021-gc35ed7a1ca22-dirty #3 PREEMPTLAZY
Tainted: [O]=OOT_MODULE, [E]=UNSIGNED_MODULE
Hardware name: IBM 3931 A01 703 (KVM/Linux)
Krnl PSW : 0704e00180000000 00000166d4853a0a (bpf_task_work_callback+0x176/0x290)
R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:2 PM:0 RI:0 EA:3
Krnl GPRS: 0400000069b02e96 000001665471856c 0000000084dc1000 000000008084da58
000000008084da60 000000005ff492bf 0000000000000000 00000000809de300
fffffffffff7ffff 00000000000a0337 00000000809e4d00 000000008437b100
00000000801bc288 00000000801bc280 00000166d48538fc 000000e6d502ba90
Krnl Code: 00000166d48539fa: e320c0400004 lg %r2,64(%r12)
00000166d4853a00: e340c0480004 lg %r4,72(%r12)
*00000166d4853a06: a7640001 brc 6,00000166d4853a08
>00000166d4853a0a: 0de1 basr %r14,%r1
00000166d4853a0c: e300b6580095 llh %r0,1624(%r11)
00000166d4853a12: ec040009027e cij %r0,2,4,00000166d4853a24
00000166d4853a18: a70affff ahi %r0,-1
00000166d4853a1c: 4000b658 sth %r0,1624(%r11)
Call Trace:
[<00000166d4853a0a>] bpf_task_work_callback+0x176/0x290
...
The disassembly contains the brc instruction (branch into the instruction
itself with two byte offset to execute an illegal instruction, and the
following basr instruction used for an indirect branch.
Reviewed-by: Jens Remus <jremus@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
---
arch/s390/Kconfig | 2 ++
1 file changed, 2 insertions(+)
diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index 84404e6778d5..ec96595cae39 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -144,6 +144,7 @@ config S390
select ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE
select ARCH_STACKWALK
select ARCH_SUPPORTS_ATOMIC_RMW
+ select ARCH_SUPPORTS_CFI
select ARCH_SUPPORTS_DEBUG_PAGEALLOC
select ARCH_SUPPORTS_HUGETLBFS
select ARCH_SUPPORTS_INT128 if CC_HAS_INT128 && CC_IS_CLANG
@@ -151,6 +152,7 @@ config S390
select ARCH_SUPPORTS_NUMA_BALANCING
select ARCH_SUPPORTS_PAGE_TABLE_CHECK
select ARCH_SUPPORTS_PER_VMA_LOCK
+ select ARCH_USES_CFI_GENERIC_LLVM_PASS if CC_IS_CLANG
select ARCH_USE_BUILTIN_BSWAP
select ARCH_USE_CMPXCHG_LOCKREF
select ARCH_USE_SYM_ANNOTATIONS
--
2.53.0
^ permalink raw reply related [flat|nested] 8+ messages in thread