Re: [PATCH v8 1/4] RISC-V: mm: Restrict address space for sv39,sv48,sv57

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On 27/07/2023 23:26, Charlie Jenkins wrote:
Make sv48 the default address space for mmap as some applications
currently depend on this assumption. A hint address passed to mmap will
cause the largest address space that fits entirely into the hint to be
used. If the hint is less than or equal to 1<<38, an sv39 address will
be used. An exception is that if the hint address is 0, then a sv48
address will be used. After an address space is completely full, the next
smallest address space will be used.

Signed-off-by: Charlie Jenkins <charlie@xxxxxxxxxxxx>
---
  arch/riscv/include/asm/elf.h       |  2 +-
  arch/riscv/include/asm/pgtable.h   | 20 +++++++++++-
  arch/riscv/include/asm/processor.h | 52 ++++++++++++++++++++++++++----
  3 files changed, 66 insertions(+), 8 deletions(-)

diff --git a/arch/riscv/include/asm/elf.h b/arch/riscv/include/asm/elf.h
index c24280774caf..5d3368d5585c 100644
--- a/arch/riscv/include/asm/elf.h
+++ b/arch/riscv/include/asm/elf.h
@@ -49,7 +49,7 @@ extern bool compat_elf_check_arch(Elf32_Ehdr *hdr);
   * the loader.  We need to make sure that it is out of the way of the program
   * that it will "exec", and that there is sufficient room for the brk.
   */
-#define ELF_ET_DYN_BASE		((TASK_SIZE / 3) * 2)
+#define ELF_ET_DYN_BASE		((DEFAULT_MAP_WINDOW / 3) * 2)
#ifdef CONFIG_64BIT
  #ifdef CONFIG_COMPAT
diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index 75970ee2bda2..c76a1ef094a4 100644
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -63,8 +63,26 @@
   * position vmemmap directly below the VMALLOC region.
   */
  #ifdef CONFIG_64BIT
+#define VA_BITS_SV39 39
+#define VA_BITS_SV48 48
+#define VA_BITS_SV57 57
+
+#define VA_USER_SV39 (UL(1) << (VA_BITS_SV39 - 1))
+#define VA_USER_SV48 (UL(1) << (VA_BITS_SV48 - 1))
+#define VA_USER_SV57 (UL(1) << (VA_BITS_SV57 - 1))
+
  #define VA_BITS		(pgtable_l5_enabled ? \
-				57 : (pgtable_l4_enabled ? 48 : 39))
+				VA_BITS_SV57 : (pgtable_l4_enabled ? VA_BITS_SV48 : VA_BITS_SV39))
+
+#ifdef CONFIG_COMPAT
+#define MMAP_VA_BITS_64 ((VA_BITS >= VA_BITS_SV48) ? VA_BITS_SV48 : VA_BITS)
+#define MMAP_MIN_VA_BITS_64 ((VA_BITS >= VA_BITS_SV39) ? VA_BITS_SV39 : VA_BITS)


Here the condition is always true right?


+#define MMAP_VA_BITS (test_thread_flag(TIF_32BIT) ? 32 : MMAP_VA_BITS_64)
+#define MMAP_MIN_VA_BITS (test_thread_flag(TIF_32BIT) ? 32 : MMAP_MIN_VA_BITS_64)


I think you should use is_compat_task() here instead of test_thread_flag(TIF_32BIT). And what about introducing VA_BITS_SV32 instead of hardcoding 32?


+#else
+#define MMAP_VA_BITS ((VA_BITS >= VA_BITS_SV48) ? VA_BITS_SV48 : VA_BITS)
+#define MMAP_MIN_VA_BITS ((VA_BITS >= VA_BITS_SV39) ? VA_BITS_SV39 : VA_BITS)


Ditto here.


+#endif
  #else
  #define VA_BITS		32
  #endif
diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h
index c950a8d9edef..e810244ea951 100644
--- a/arch/riscv/include/asm/processor.h
+++ b/arch/riscv/include/asm/processor.h
@@ -13,19 +13,59 @@
#include <asm/ptrace.h> +#ifdef CONFIG_64BIT
+#define DEFAULT_MAP_WINDOW	(UL(1) << (MMAP_VA_BITS - 1))
+#define STACK_TOP_MAX		TASK_SIZE_64
+
+#define arch_get_mmap_end(addr, len, flags)	\
+({	\
+	unsigned long mmap_end;	\
+	typeof(addr) _addr = (addr); \
+	if ((_addr) == 0 || (IS_ENABLED(CONFIG_COMPAT) && test_thread_flag(TIF_32BIT))) \
+		mmap_end = DEFAULT_MAP_WINDOW;	\


Wouldn't that prevent a sv57 system to allocate sv57 addresses when sv48 is full unless explicitly asked?


+	else if ((_addr) >= VA_USER_SV57)	\
+		mmap_end = STACK_TOP_MAX;	\
+	else if ((((_addr) >= VA_USER_SV48)) && (VA_BITS >= VA_BITS_SV48))	\
+		mmap_end = VA_USER_SV48;	\
+	else	\
+		mmap_end = VA_USER_SV39;	\
+	mmap_end;	\
+})
+
+#define arch_get_mmap_base(addr, base) \
+({ \
+	unsigned long mmap_base; \
+	typeof(addr) _addr = (addr); \
+	typeof(base) _base = (base); \
+	unsigned long rnd_gap = (_base) - DEFAULT_MAP_WINDOW; \
+	if ((_addr) == 0 || (IS_ENABLED(CONFIG_COMPAT) && test_thread_flag(TIF_32BIT))) \
+		mmap_base = (_base); \
+	else if (((_addr) >= VA_USER_SV57) && (VA_BITS >= VA_BITS_SV57)) \
+		mmap_base = VA_USER_SV57 + rnd_gap; \


Shouldn't it be mmap_base = VA_USER_SV57 - rnd_gap?


+	else if ((((_addr) >= VA_USER_SV48)) && (VA_BITS >= VA_BITS_SV48)) \
+		mmap_base = VA_USER_SV48 + rnd_gap; \
+	else \
+		mmap_base = VA_USER_SV39 + rnd_gap; \
+	mmap_base; \
+})
+
+#else
+#define DEFAULT_MAP_WINDOW	TASK_SIZE
+#define STACK_TOP_MAX		TASK_SIZE
+#endif
+#define STACK_ALIGN		16
+
+#define STACK_TOP		DEFAULT_MAP_WINDOW
+
  /*
   * This decides where the kernel will search for a free chunk of vm
   * space during mmap's.
   */
-#define TASK_UNMAPPED_BASE	PAGE_ALIGN(TASK_SIZE / 3)
-
-#define STACK_TOP		TASK_SIZE
  #ifdef CONFIG_64BIT
-#define STACK_TOP_MAX		TASK_SIZE_64
+#define TASK_UNMAPPED_BASE	PAGE_ALIGN((UL(1) << MMAP_MIN_VA_BITS) / 3)
  #else
-#define STACK_TOP_MAX		TASK_SIZE
+#define TASK_UNMAPPED_BASE	PAGE_ALIGN(TASK_SIZE / 3)
  #endif
-#define STACK_ALIGN		16
#ifndef __ASSEMBLY__



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