RISC-V: Add support for rv32 userspace via COMPAT

The RISC-V port supports the rv32i and rv64i base ISAs, but provides no
mechanism to run 32-bit userspace on 64-bit systems.  This adds that
support, via the COMPAT framework.  As the RISC-V ISAs (and uABIs) were
developed concurrently, the resulting compat support is mostly generic.

This includes a handful of cleanups to the generic compat infrastructure
to more cleanly support RISC-V, followed by the RISC-V implementation.

* palmer/riscv-compat:
  riscv: compat: Add COMPAT Kbuild skeletal support
  riscv: compat: ptrace: Add compat_arch_ptrace implement
  riscv: compat: signal: Add rt_frame implementation
  riscv: compat: vdso: Add setup additional pages implementation
  riscv: compat: vdso: Add COMPAT_VDSO base code implementation
  riscv: compat: Add hw capability check for elf
  riscv: compat: Add elf.h implementation
  riscv: compat: process: Add UXL_32 support in start_thread
  riscv: compat: syscall: Add entry.S implementation
  riscv: compat: syscall: Add compat_sys_call_table implementation
  riscv: compat: Support TASK_SIZE for compat mode
  riscv: compat: Add basic compat data type implementation
  riscv: Fixup difference with defconfig
  syscalls: compat: Fix the missing part for __SYSCALL_COMPAT
  asm-generic: compat: Cleanup duplicate definitions
  fs: stat: compat: Add __ARCH_WANT_COMPAT_STAT
  arch: Add SYSVIPC_COMPAT for all architectures
  compat: consolidate the compat_flock{,64} definition
  uapi: always define F_GETLK64/F_SETLK64/F_SETLKW64 in fcntl.h
  uapi: simplify __ARCH_FLOCK{,64}_PAD a little

12 files changed, 242 insertions, 6 deletions

diff --git a/arch/riscv/include/asm/compat.h b/arch/riscv/include/asm/compat.h
new file mode 100644
index 000000000000..2ac955b51148
--- /dev/null
+++ b/arch/riscv/include/asm/compat.h
@@ -0,0 +1,129 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef __ASM_COMPAT_H
+#define __ASM_COMPAT_H
+
+#define COMPAT_UTS_MACHINE	"riscv\0\0"
+
+/*
+ * Architecture specific compatibility types
+ */
+#include <linux/types.h>
+#include <linux/sched.h>
+#include <linux/sched/task_stack.h>
+#include <asm-generic/compat.h>
+
+static inline int is_compat_task(void)
+{
+	return test_thread_flag(TIF_32BIT);
+}
+
+struct compat_user_regs_struct {
+	compat_ulong_t pc;
+	compat_ulong_t ra;
+	compat_ulong_t sp;
+	compat_ulong_t gp;
+	compat_ulong_t tp;
+	compat_ulong_t t0;
+	compat_ulong_t t1;
+	compat_ulong_t t2;
+	compat_ulong_t s0;
+	compat_ulong_t s1;
+	compat_ulong_t a0;
+	compat_ulong_t a1;
+	compat_ulong_t a2;
+	compat_ulong_t a3;
+	compat_ulong_t a4;
+	compat_ulong_t a5;
+	compat_ulong_t a6;
+	compat_ulong_t a7;
+	compat_ulong_t s2;
+	compat_ulong_t s3;
+	compat_ulong_t s4;
+	compat_ulong_t s5;
+	compat_ulong_t s6;
+	compat_ulong_t s7;
+	compat_ulong_t s8;
+	compat_ulong_t s9;
+	compat_ulong_t s10;
+	compat_ulong_t s11;
+	compat_ulong_t t3;
+	compat_ulong_t t4;
+	compat_ulong_t t5;
+	compat_ulong_t t6;
+};
+
+static inline void regs_to_cregs(struct compat_user_regs_struct *cregs,
+				 struct pt_regs *regs)
+{
+	cregs->pc	= (compat_ulong_t) regs->epc;
+	cregs->ra	= (compat_ulong_t) regs->ra;
+	cregs->sp	= (compat_ulong_t) regs->sp;
+	cregs->gp	= (compat_ulong_t) regs->gp;
+	cregs->tp	= (compat_ulong_t) regs->tp;
+	cregs->t0	= (compat_ulong_t) regs->t0;
+	cregs->t1	= (compat_ulong_t) regs->t1;
+	cregs->t2	= (compat_ulong_t) regs->t2;
+	cregs->s0	= (compat_ulong_t) regs->s0;
+	cregs->s1	= (compat_ulong_t) regs->s1;
+	cregs->a0	= (compat_ulong_t) regs->a0;
+	cregs->a1	= (compat_ulong_t) regs->a1;
+	cregs->a2	= (compat_ulong_t) regs->a2;
+	cregs->a3	= (compat_ulong_t) regs->a3;
+	cregs->a4	= (compat_ulong_t) regs->a4;
+	cregs->a5	= (compat_ulong_t) regs->a5;
+	cregs->a6	= (compat_ulong_t) regs->a6;
+	cregs->a7	= (compat_ulong_t) regs->a7;
+	cregs->s2	= (compat_ulong_t) regs->s2;
+	cregs->s3	= (compat_ulong_t) regs->s3;
+	cregs->s4	= (compat_ulong_t) regs->s4;
+	cregs->s5	= (compat_ulong_t) regs->s5;
+	cregs->s6	= (compat_ulong_t) regs->s6;
+	cregs->s7	= (compat_ulong_t) regs->s7;
+	cregs->s8	= (compat_ulong_t) regs->s8;
+	cregs->s9	= (compat_ulong_t) regs->s9;
+	cregs->s10	= (compat_ulong_t) regs->s10;
+	cregs->s11	= (compat_ulong_t) regs->s11;
+	cregs->t3	= (compat_ulong_t) regs->t3;
+	cregs->t4	= (compat_ulong_t) regs->t4;
+	cregs->t5	= (compat_ulong_t) regs->t5;
+	cregs->t6	= (compat_ulong_t) regs->t6;
+};
+
+static inline void cregs_to_regs(struct compat_user_regs_struct *cregs,
+				 struct pt_regs *regs)
+{
+	regs->epc	= (unsigned long) cregs->pc;
+	regs->ra	= (unsigned long) cregs->ra;
+	regs->sp	= (unsigned long) cregs->sp;
+	regs->gp	= (unsigned long) cregs->gp;
+	regs->tp	= (unsigned long) cregs->tp;
+	regs->t0	= (unsigned long) cregs->t0;
+	regs->t1	= (unsigned long) cregs->t1;
+	regs->t2	= (unsigned long) cregs->t2;
+	regs->s0	= (unsigned long) cregs->s0;
+	regs->s1	= (unsigned long) cregs->s1;
+	regs->a0	= (unsigned long) cregs->a0;
+	regs->a1	= (unsigned long) cregs->a1;
+	regs->a2	= (unsigned long) cregs->a2;
+	regs->a3	= (unsigned long) cregs->a3;
+	regs->a4	= (unsigned long) cregs->a4;
+	regs->a5	= (unsigned long) cregs->a5;
+	regs->a6	= (unsigned long) cregs->a6;
+	regs->a7	= (unsigned long) cregs->a7;
+	regs->s2	= (unsigned long) cregs->s2;
+	regs->s3	= (unsigned long) cregs->s3;
+	regs->s4	= (unsigned long) cregs->s4;
+	regs->s5	= (unsigned long) cregs->s5;
+	regs->s6	= (unsigned long) cregs->s6;
+	regs->s7	= (unsigned long) cregs->s7;
+	regs->s8	= (unsigned long) cregs->s8;
+	regs->s9	= (unsigned long) cregs->s9;
+	regs->s10	= (unsigned long) cregs->s10;
+	regs->s11	= (unsigned long) cregs->s11;
+	regs->t3	= (unsigned long) cregs->t3;
+	regs->t4	= (unsigned long) cregs->t4;
+	regs->t5	= (unsigned long) cregs->t5;
+	regs->t6	= (unsigned long) cregs->t6;
+};
+
+#endif /* __ASM_COMPAT_H */
diff --git a/arch/riscv/include/asm/csr.h b/arch/riscv/include/asm/csr.h
index e935f27b10fd..f5d1251fd6c7 100644
--- a/arch/riscv/include/asm/csr.h
+++ b/arch/riscv/include/asm/csr.h
@@ -36,6 +36,13 @@
 #define SR_SD		_AC(0x8000000000000000, UL) /* FS/XS dirty */
 #endif
 
+#ifdef CONFIG_64BIT
+#define SR_UXL		_AC(0x300000000, UL) /* XLEN mask for U-mode */
+#define SR_UXL_32	_AC(0x100000000, UL) /* XLEN = 32 for U-mode */
+#define SR_UXL_64	_AC(0x200000000, UL) /* XLEN = 64 for U-mode */
+#define SR_UXL_SHIFT	32
+#endif
+
 /* SATP flags */
 #ifndef CONFIG_64BIT
 #define SATP_PPN	_AC(0x003FFFFF, UL)
diff --git a/arch/riscv/include/asm/elf.h b/arch/riscv/include/asm/elf.h
index f53c40026c7a..14fc7342490b 100644
--- a/arch/riscv/include/asm/elf.h
+++ b/arch/riscv/include/asm/elf.h
@@ -8,6 +8,8 @@
 #ifndef _ASM_RISCV_ELF_H
 #define _ASM_RISCV_ELF_H
 
+#include <uapi/linux/elf.h>
+#include <linux/compat.h>
 #include <uapi/asm/elf.h>
 #include <asm/auxvec.h>
 #include <asm/byteorder.h>
@@ -18,18 +20,24 @@
  */
 #define ELF_ARCH	EM_RISCV
 
+#ifndef ELF_CLASS
 #ifdef CONFIG_64BIT
 #define ELF_CLASS	ELFCLASS64
 #else
 #define ELF_CLASS	ELFCLASS32
 #endif
+#endif
 
 #define ELF_DATA	ELFDATA2LSB
 
 /*
  * This is used to ensure we don't load something for the wrong architecture.
  */
-#define elf_check_arch(x) ((x)->e_machine == EM_RISCV)
+#define elf_check_arch(x) (((x)->e_machine == EM_RISCV) && \
+			   ((x)->e_ident[EI_CLASS] == ELF_CLASS))
+
+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_EXEC_PAGESIZE	(PAGE_SIZE)
@@ -43,8 +51,14 @@
 #define ELF_ET_DYN_BASE		((TASK_SIZE / 3) * 2)
 
 #ifdef CONFIG_64BIT
+#ifdef CONFIG_COMPAT
+#define STACK_RND_MASK		(test_thread_flag(TIF_32BIT) ? \
+				 0x7ff >> (PAGE_SHIFT - 12) : \
+				 0x3ffff >> (PAGE_SHIFT - 12))
+#else
 #define STACK_RND_MASK		(0x3ffff >> (PAGE_SHIFT - 12))
 #endif
+#endif
 /*
  * This yields a mask that user programs can use to figure out what
  * instruction set this CPU supports.  This could be done in user space,
@@ -60,11 +74,19 @@ extern unsigned long elf_hwcap;
  */
 #define ELF_PLATFORM	(NULL)
 
+#define COMPAT_ELF_PLATFORM	(NULL)
+
 #ifdef CONFIG_MMU
 #define ARCH_DLINFO						\
 do {								\
+	/*							\
+	 * Note that we add ulong after elf_addr_t because	\
+	 * casting current->mm->context.vdso triggers a cast	\
+	 * warning of cast from pointer to integer for		\
+	 * COMPAT ELFCLASS32.					\
+	 */							\
 	NEW_AUX_ENT(AT_SYSINFO_EHDR,				\
-		(elf_addr_t)current->mm->context.vdso);		\
+		(elf_addr_t)(ulong)current->mm->context.vdso);	\
 	NEW_AUX_ENT(AT_L1I_CACHESIZE,				\
 		get_cache_size(1, CACHE_TYPE_INST));		\
 	NEW_AUX_ENT(AT_L1I_CACHEGEOMETRY,			\
@@ -90,4 +112,28 @@ do {							\
 		*(struct user_regs_struct *)regs;	\
 } while (0);
 
+#ifdef CONFIG_COMPAT
+
+#define SET_PERSONALITY(ex)					\
+do {    if ((ex).e_ident[EI_CLASS] == ELFCLASS32)		\
+		set_thread_flag(TIF_32BIT);			\
+	else							\
+		clear_thread_flag(TIF_32BIT);			\
+	if (personality(current->personality) != PER_LINUX32)	\
+		set_personality(PER_LINUX |			\
+			(current->personality & (~PER_MASK)));	\
+} while (0)
+
+#define COMPAT_ELF_ET_DYN_BASE		((TASK_SIZE_32 / 3) * 2)
+
+/* rv32 registers */
+typedef compat_ulong_t			compat_elf_greg_t;
+typedef compat_elf_greg_t		compat_elf_gregset_t[ELF_NGREG];
+
+extern int compat_arch_setup_additional_pages(struct linux_binprm *bprm,
+					      int uses_interp);
+#define compat_arch_setup_additional_pages \
+				compat_arch_setup_additional_pages
+
+#endif /* CONFIG_COMPAT */
 #endif /* _ASM_RISCV_ELF_H */
diff --git a/arch/riscv/include/asm/mmu.h b/arch/riscv/include/asm/mmu.h
index 0099dc116168..cedcf8ea3c76 100644
--- a/arch/riscv/include/asm/mmu.h
+++ b/arch/riscv/include/asm/mmu.h
@@ -16,6 +16,7 @@ typedef struct {
 	atomic_long_t id;
 #endif
 	void *vdso;
+	void *vdso_info;
 #ifdef CONFIG_SMP
 	/* A local icache flush is needed before user execution can resume. */
 	cpumask_t icache_stale_mask;
diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index 6f0a260d3f2c..eefaab1d3535 100644
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -740,8 +740,17 @@ static inline pmd_t pmdp_establish(struct vm_area_struct *vma,
  * 63–48 all equal to bit 47, or else a page-fault exception will occur."
  */
 #ifdef CONFIG_64BIT
-#define TASK_SIZE      (PGDIR_SIZE * PTRS_PER_PGD / 2)
-#define TASK_SIZE_MIN  (PGDIR_SIZE_L3 * PTRS_PER_PGD / 2)
+#define TASK_SIZE_64	(PGDIR_SIZE * PTRS_PER_PGD / 2)
+#define TASK_SIZE_MIN	(PGDIR_SIZE_L3 * PTRS_PER_PGD / 2)
+
+#ifdef CONFIG_COMPAT
+#define TASK_SIZE_32	(_AC(0x80000000, UL) - PAGE_SIZE)
+#define TASK_SIZE	(test_thread_flag(TIF_32BIT) ? \
+			 TASK_SIZE_32 : TASK_SIZE_64)
+#else
+#define TASK_SIZE	TASK_SIZE_64
+#endif
+
 #else
 #define TASK_SIZE	FIXADDR_START
 #define TASK_SIZE_MIN	TASK_SIZE
diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h
index 0749924d9e55..21c8072dce17 100644
--- a/arch/riscv/include/asm/processor.h
+++ b/arch/riscv/include/asm/processor.h
@@ -19,7 +19,11 @@
 #define TASK_UNMAPPED_BASE	PAGE_ALIGN(TASK_SIZE / 3)
 
 #define STACK_TOP		TASK_SIZE
-#define STACK_TOP_MAX		STACK_TOP
+#ifdef CONFIG_64BIT
+#define STACK_TOP_MAX		TASK_SIZE_64
+#else
+#define STACK_TOP_MAX		TASK_SIZE
+#endif
 #define STACK_ALIGN		16
 
 #ifndef __ASSEMBLY__
diff --git a/arch/riscv/include/asm/signal32.h b/arch/riscv/include/asm/signal32.h
new file mode 100644
index 000000000000..96dc56932e76
--- /dev/null
+++ b/arch/riscv/include/asm/signal32.h
@@ -0,0 +1,18 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#ifndef __ASM_SIGNAL32_H
+#define __ASM_SIGNAL32_H
+
+#if IS_ENABLED(CONFIG_COMPAT)
+int compat_setup_rt_frame(struct ksignal *ksig, sigset_t *set,
+			  struct pt_regs *regs);
+#else
+static inline
+int compat_setup_rt_frame(struct ksignal *ksig, sigset_t *set,
+			  struct pt_regs *regs)
+{
+	return -1;
+}
+#endif
+
+#endif
diff --git a/arch/riscv/include/asm/syscall.h b/arch/riscv/include/asm/syscall.h
index 7ac6a0e275f2..384a63b86420 100644
--- a/arch/riscv/include/asm/syscall.h
+++ b/arch/riscv/include/asm/syscall.h
@@ -16,6 +16,7 @@
 
 /* The array of function pointers for syscalls. */
 extern void * const sys_call_table[];
+extern void * const compat_sys_call_table[];
 
 /*
  * Only the low 32 bits of orig_r0 are meaningful, so we return int.
diff --git a/arch/riscv/include/asm/thread_info.h b/arch/riscv/include/asm/thread_info.h
index 74d888c8d631..78933ac04995 100644
--- a/arch/riscv/include/asm/thread_info.h
+++ b/arch/riscv/include/asm/thread_info.h
@@ -97,6 +97,7 @@ struct thread_info {
 #define TIF_SECCOMP		8	/* syscall secure computing */
 #define TIF_NOTIFY_SIGNAL	9	/* signal notifications exist */
 #define TIF_UPROBE		10	/* uprobe breakpoint or singlestep */
+#define TIF_32BIT		11	/* compat-mode 32bit process */
 
 #define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)
 #define _TIF_NOTIFY_RESUME	(1 << TIF_NOTIFY_RESUME)
diff --git a/arch/riscv/include/asm/unistd.h b/arch/riscv/include/asm/unistd.h
index 6c316093a1e5..5ddac412b578 100644
--- a/arch/riscv/include/asm/unistd.h
+++ b/arch/riscv/include/asm/unistd.h
@@ -11,6 +11,17 @@
 #define __ARCH_WANT_SYS_CLONE
 #define __ARCH_WANT_MEMFD_SECRET
 
+#ifdef CONFIG_COMPAT
+#define __ARCH_WANT_COMPAT_TRUNCATE64
+#define __ARCH_WANT_COMPAT_FTRUNCATE64
+#define __ARCH_WANT_COMPAT_FALLOCATE
+#define __ARCH_WANT_COMPAT_PREAD64
+#define __ARCH_WANT_COMPAT_PWRITE64
+#define __ARCH_WANT_COMPAT_SYNC_FILE_RANGE
+#define __ARCH_WANT_COMPAT_READAHEAD
+#define __ARCH_WANT_COMPAT_FADVISE64_64
+#endif
+
 #include <uapi/asm/unistd.h>
 
 #define NR_syscalls (__NR_syscalls)
diff --git a/arch/riscv/include/asm/vdso.h b/arch/riscv/include/asm/vdso.h
index bc6f75f3a199..af981426fe0f 100644
--- a/arch/riscv/include/asm/vdso.h
+++ b/arch/riscv/include/asm/vdso.h
@@ -21,6 +21,15 @@
 
 #define VDSO_SYMBOL(base, name)							\
 	(void __user *)((unsigned long)(base) + __vdso_##name##_offset)
+
+#ifdef CONFIG_COMPAT
+#include <generated/compat_vdso-offsets.h>
+
+#define COMPAT_VDSO_SYMBOL(base, name)						\
+	(void __user *)((unsigned long)(base) + compat__vdso_##name##_offset)
+
+#endif /* CONFIG_COMPAT */
+
 #endif /* !__ASSEMBLY__ */
 
 #endif /* CONFIG_MMU */
diff --git a/arch/riscv/include/uapi/asm/unistd.h b/arch/riscv/include/uapi/asm/unistd.h
index 8062996c2dfd..c9e50eed14aa 100644
--- a/arch/riscv/include/uapi/asm/unistd.h
+++ b/arch/riscv/include/uapi/asm/unistd.h
@@ -15,7 +15,7 @@
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  */
 
-#ifdef __LP64__
+#if defined(__LP64__) && !defined(__SYSCALL_COMPAT)
 #define __ARCH_WANT_NEW_STAT
 #define __ARCH_WANT_SET_GET_RLIMIT
 #endif /* __LP64__ */