riscv: support the elf-fdpic binfmt loader

Add support for enabling and using the binfmt_elf_fdpic program loader
on RISC-V platforms. The most important change is to setup registers
during program load to pass the mapping addresses to the new process.

One of the interesting features of the elf-fdpic loader is that it
also allows appropriately compiled ELF format binaries to be loaded on
nommu systems. Appropriate being those compiled with -pie.

Signed-off-by: Greg Ungerer <gerg@kernel.org>
Acked-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20230711130754.481209-3-gerg@kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

diff --git a/arch/riscv/include/asm/elf.h b/arch/riscv/include/asm/elf.h
index c242807..c33fe92 100644 (file)
--- a/arch/riscv/include/asm/elf.h
+++ b/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,

diff --git a/arch/riscv/include/asm/mmu.h b/arch/riscv/include/asm/mmu.h
index 0099dc1..355504b 100644 (file)
--- a/arch/riscv/include/asm/mmu.h
+++ b/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,

diff --git a/arch/riscv/include/uapi/asm/ptrace.h b/arch/riscv/include/uapi/asm/ptrace.h
index e17c550..30f6d65 100644 (file)
--- a/arch/riscv/include/uapi/asm/ptrace.h
+++ b/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
  *

diff --git a/fs/Kconfig.binfmt b/fs/Kconfig.binfmt
index 93539aa..f569316 100644 (file)
--- a/fs/Kconfig.binfmt
+++ b/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