Merge patch series "riscv: support ELF format binaries in nommu mode"

Greg Ungerer <gerg@kernel.org> says:

The following changes add the ability to run ELF format binaries when
running RISC-V in nommu mode. That support is actually part of the
ELF-FDPIC loader, so these changes are all about making that work on
RISC-V.

The first issue to deal with is making the ELF-FDPIC loader capable of
handling 64-bit ELF files. As coded right now it only supports 32-bit
ELF files.

Secondly some changes are required to enable and compile the ELF-FDPIC
loader on RISC-V and to pass the ELF-FDPIC mapping addresses through to
user space when execing the new program.

These changes have not been used to run actual ELF-FDPIC binaries.
It is used to load and run normal ELF - compiled -pie format. Though the
underlying changes are expected to work with full ELF-FDPIC binaries if
or when that is supported on RISC-V in gcc.

To avoid needing changes to the C-library (tested with uClibc-ng
currently) there is a simple runtime dynamic loader (interpreter)
available to do the final relocations, https://github.com/gregungerer/uldso.
The nice thing about doing it this way is that the same program
binary can also be loaded with the usual ELF loader in MMU linux.

The motivation here is to provide an easy to use alternative to the
flat format binaries normally used for RISC-V nommu based systems.

* b4-shazam-merge:
  riscv: support the elf-fdpic binfmt loader
  binfmt_elf_fdpic: support 64-bit systems

Link: https://lore.kernel.org/r/20230711130754.481209-1-gerg@kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

Author: palmer-dabbelt

arch/riscv/include/asm/elf.h

@@ -41,6 +41,7 @@ extern bool compat_elf_check_arch(Elf32_Ehdr *hdr);
 #define compat_elf_check_arch	compat_elf_check_arch
 
 #define CORE_DUMP_USE_REGSET
+#define ELF_FDPIC_CORE_EFLAGS	0
 #define ELF_EXEC_PAGESIZE	(PAGE_SIZE)
 
 /*
@@ -69,6 +70,13 @@ extern bool compat_elf_check_arch(Elf32_Ehdr *hdr);
 #define ELF_HWCAP	riscv_get_elf_hwcap()
 extern unsigned long elf_hwcap;
 
+#define ELF_FDPIC_PLAT_INIT(_r, _exec_map_addr, _interp_map_addr, dynamic_addr) \
+	do { \
+		(_r)->a1 = _exec_map_addr; \
+		(_r)->a2 = _interp_map_addr; \
+		(_r)->a3 = dynamic_addr; \
+	} while (0)
+
 /*
  * This yields a string that ld.so will use to load implementation
  * specific libraries for optimization.  This is more specific in
@@ -78,7 +86,6 @@ extern unsigned long elf_hwcap;
 
 #define COMPAT_ELF_PLATFORM	(NULL)
 
-#ifdef CONFIG_MMU
 #define ARCH_DLINFO						\
 do {								\
 	/*							\
@@ -115,6 +122,8 @@ do {								\
 	else							 \
 		NEW_AUX_ENT(AT_IGNORE, 0);			 \
 } while (0)
+
+#ifdef CONFIG_MMU
 #define ARCH_HAS_SETUP_ADDITIONAL_PAGES
 struct linux_binprm;
 extern int arch_setup_additional_pages(struct linux_binprm *bprm,

arch/riscv/include/asm/mmu.h

@@ -20,6 +20,10 @@ typedef struct {
 	/* A local icache flush is needed before user execution can resume. */
 	cpumask_t icache_stale_mask;
 #endif
+#ifdef CONFIG_BINFMT_ELF_FDPIC
+	unsigned long exec_fdpic_loadmap;
+	unsigned long interp_fdpic_loadmap;
+#endif
 } mm_context_t;
 
 void __init create_pgd_mapping(pgd_t *pgdp, uintptr_t va, phys_addr_t pa,

arch/riscv/include/uapi/asm/ptrace.h

@@ -10,6 +10,11 @@
 
 #include <linux/types.h>
 
+#define PTRACE_GETFDPIC		33
+
+#define PTRACE_GETFDPIC_EXEC	0
+#define PTRACE_GETFDPIC_INTERP	1
+
 /*
  * User-mode register state for core dumps, ptrace, sigcontext
  *

fs/Kconfig.binfmt

@@ -58,7 +58,7 @@ config ARCH_USE_GNU_PROPERTY
 config BINFMT_ELF_FDPIC
 	bool "Kernel support for FDPIC ELF binaries"
 	default y if !BINFMT_ELF
-	depends on ARM || ((M68K || SUPERH || XTENSA) && !MMU)
+	depends on ARM || ((M68K || RISCV || SUPERH || XTENSA) && !MMU)
 	select ELFCORE
 	help
 	  ELF FDPIC binaries are based on ELF, but allow the individual load

fs/binfmt_elf_fdpic.c

@@ -138,7 +138,7 @@ static int is_constdisp(struct elfhdr *hdr)
 static int elf_fdpic_fetch_phdrs(struct elf_fdpic_params *params,
 				 struct file *file)
 {
-	struct elf32_phdr *phdr;
+	struct elf_phdr *phdr;
 	unsigned long size;
 	int retval, loop;
 	loff_t pos = params->hdr.e_phoff;
@@ -560,8 +560,8 @@ static int create_elf_fdpic_tables(struct linux_binprm *bprm,
 	sp &= ~7UL;
 
 	/* stack the load map(s) */
-	len = sizeof(struct elf32_fdpic_loadmap);
-	len += sizeof(struct elf32_fdpic_loadseg) * exec_params->loadmap->nsegs;
+	len = sizeof(struct elf_fdpic_loadmap);
+	len += sizeof(struct elf_fdpic_loadseg) * exec_params->loadmap->nsegs;
 	sp = (sp - len) & ~7UL;
 	exec_params->map_addr = sp;
 
@@ -571,8 +571,8 @@ static int create_elf_fdpic_tables(struct linux_binprm *bprm,
 	current->mm->context.exec_fdpic_loadmap = (unsigned long) sp;
 
 	if (interp_params->loadmap) {
-		len = sizeof(struct elf32_fdpic_loadmap);
-		len += sizeof(struct elf32_fdpic_loadseg) *
+		len = sizeof(struct elf_fdpic_loadmap);
+		len += sizeof(struct elf_fdpic_loadseg) *
 			interp_params->loadmap->nsegs;
 		sp = (sp - len) & ~7UL;
 		interp_params->map_addr = sp;
@@ -740,13 +740,13 @@ static int elf_fdpic_map_file(struct elf_fdpic_params *params,
 			      struct mm_struct *mm,
 			      const char *what)
 {
-	struct elf32_fdpic_loadmap *loadmap;
+	struct elf_fdpic_loadmap *loadmap;
 #ifdef CONFIG_MMU
-	struct elf32_fdpic_loadseg *mseg;
+	struct elf_fdpic_loadseg *mseg;
 	unsigned long load_addr;
 #endif
-	struct elf32_fdpic_loadseg *seg;
-	struct elf32_phdr *phdr;
+	struct elf_fdpic_loadseg *seg;
+	struct elf_phdr *phdr;
 	unsigned nloads, tmp;
 	unsigned long stop;
 	int loop, ret;
@@ -766,7 +766,7 @@ static int elf_fdpic_map_file(struct elf_fdpic_params *params,
 
 	params->loadmap = loadmap;
 
-	loadmap->version = ELF32_FDPIC_LOADMAP_VERSION;
+	loadmap->version = ELF_FDPIC_LOADMAP_VERSION;
 	loadmap->nsegs = nloads;
 
 	/* map the requested LOADs into the memory space */
@@ -839,8 +839,8 @@ static int elf_fdpic_map_file(struct elf_fdpic_params *params,
 			if (phdr->p_vaddr >= seg->p_vaddr &&
 			    phdr->p_vaddr + phdr->p_memsz <=
 			    seg->p_vaddr + seg->p_memsz) {
-				Elf32_Dyn __user *dyn;
-				Elf32_Sword d_tag;
+				Elf_Dyn __user *dyn;
+				Elf_Sword d_tag;
 
 				params->dynamic_addr =
 					(phdr->p_vaddr - seg->p_vaddr) +
@@ -850,11 +850,11 @@ static int elf_fdpic_map_file(struct elf_fdpic_params *params,
 				 * one item, and that the last item is a NULL
 				 * entry */
 				if (phdr->p_memsz == 0 ||
-				    phdr->p_memsz % sizeof(Elf32_Dyn) != 0)
+				    phdr->p_memsz % sizeof(Elf_Dyn) != 0)
 					goto dynamic_error;
 
-				tmp = phdr->p_memsz / sizeof(Elf32_Dyn);
-				dyn = (Elf32_Dyn __user *)params->dynamic_addr;
+				tmp = phdr->p_memsz / sizeof(Elf_Dyn);
+				dyn = (Elf_Dyn __user *)params->dynamic_addr;
 				if (get_user(d_tag, &dyn[tmp - 1].d_tag) ||
 				    d_tag != 0)
 					goto dynamic_error;
@@ -923,8 +923,8 @@ static int elf_fdpic_map_file_constdisp_on_uclinux(
 	struct file *file,
 	struct mm_struct *mm)
 {
-	struct elf32_fdpic_loadseg *seg;
-	struct elf32_phdr *phdr;
+	struct elf_fdpic_loadseg *seg;
+	struct elf_phdr *phdr;
 	unsigned long load_addr, base = ULONG_MAX, top = 0, maddr = 0;
 	int loop, ret;
 
@@ -1007,8 +1007,8 @@ static int elf_fdpic_map_file_by_direct_mmap(struct elf_fdpic_params *params,
 					     struct file *file,
 					     struct mm_struct *mm)
 {
-	struct elf32_fdpic_loadseg *seg;
-	struct elf32_phdr *phdr;
+	struct elf_fdpic_loadseg *seg;
+	struct elf_phdr *phdr;
 	unsigned long load_addr, delta_vaddr;
 	int loop, dvset;
 

include/linux/elf-fdpic.h

@@ -10,13 +10,25 @@
 
 #include <uapi/linux/elf-fdpic.h>
 
+#if ELF_CLASS == ELFCLASS32
+#define Elf_Sword			Elf32_Sword
+#define elf_fdpic_loadseg		elf32_fdpic_loadseg
+#define elf_fdpic_loadmap		elf32_fdpic_loadmap
+#define ELF_FDPIC_LOADMAP_VERSION	ELF32_FDPIC_LOADMAP_VERSION
+#else
+#define Elf_Sword			Elf64_Sxword
+#define elf_fdpic_loadmap		elf64_fdpic_loadmap
+#define elf_fdpic_loadseg		elf64_fdpic_loadseg
+#define ELF_FDPIC_LOADMAP_VERSION	ELF64_FDPIC_LOADMAP_VERSION
+#endif
+
 /*
  * binfmt binary parameters structure
  */
 struct elf_fdpic_params {
 	struct elfhdr			hdr;		/* ref copy of ELF header */
 	struct elf_phdr			*phdrs;		/* ref copy of PT_PHDR table */
-	struct elf32_fdpic_loadmap	*loadmap;	/* loadmap to be passed to userspace */
+	struct elf_fdpic_loadmap	*loadmap;	/* loadmap to be passed to userspace */
 	unsigned long			elfhdr_addr;	/* mapped ELF header user address */
 	unsigned long			ph_addr;	/* mapped PT_PHDR user address */
 	unsigned long			map_addr;	/* mapped loadmap user address */

include/uapi/linux/elf-fdpic.h

@@ -32,4 +32,19 @@ struct elf32_fdpic_loadmap {
 
 #define ELF32_FDPIC_LOADMAP_VERSION	0x0000
 
+/* segment mappings for ELF FDPIC libraries/executables/interpreters */
+struct elf64_fdpic_loadseg {
+	Elf64_Addr	addr;		/* core address to which mapped */
+	Elf64_Addr	p_vaddr;	/* VMA recorded in file */
+	Elf64_Word	p_memsz;	/* allocation size recorded in file */
+};
+
+struct elf64_fdpic_loadmap {
+	Elf64_Half	version;	/* version of these structures, just in case... */
+	Elf64_Half	nsegs;		/* number of segments */
+	struct elf64_fdpic_loadseg segs[];
+};
+
+#define ELF64_FDPIC_LOADMAP_VERSION	0x0000
+
 #endif /* _UAPI_LINUX_ELF_FDPIC_H */