On Thu, Apr 10, 2025 at 12:03:44PM +0200, Radim Krčmář wrote:
2025-03-14T14:39:25-07:00, Deepak Gupta <de...@rivosinc.com>:
diff --git a/arch/riscv/include/asm/mman.h b/arch/riscv/include/asm/mman.h
+static inline unsigned long arch_calc_vm_prot_bits(unsigned long prot,
+ unsigned long pkey
__always_unused)
+{
+ unsigned long ret = 0;
+
+ /*
+ * If PROT_WRITE was specified, force it to VM_READ | VM_WRITE.
+ * Only VM_WRITE means shadow stack.
+ */
This function also changes PROT_WX to VM_RWX, which is effectively not
changing anything, but I think it deserves an explicit intent.
(At least in the commit message.)
Will do that.
+ if (prot & PROT_WRITE)
+ ret = (VM_READ | VM_WRITE);
+ return ret;
+}
diff --git a/arch/riscv/kernel/sys_riscv.c b/arch/riscv/kernel/sys_riscv.c
@@ -16,6 +17,15 @@ static long riscv_sys_mmap(unsigned long addr, unsigned long
len,
+ /*
+ * If PROT_WRITE is specified then extend that to PROT_READ
+ * protection_map[VM_WRITE] is now going to select shadow stack
encodings.
+ * So specifying PROT_WRITE actually should select protection_map
[VM_WRITE | VM_READ]
+ * If user wants to create shadow stack then they should use
`map_shadow_stack` syscall.
+ */
+ if (unlikely((prot & PROT_WRITE) && !(prot & PROT_READ)))
+ prot |= PROT_READ;
Why isn't the previous hunk be enough? (Or why don't we do just this?)
riscv_sys_mmap() eventually calls arch_calc_vm_prot_bits(), so I'd
rather fix each code path just once.
You're right. Above hunk (arch/riscv/include/asm/mman.h) alone should be enough.
I did this change in `sys_riscv.c` out of caution. If it feels like
un-necessary,
I'll remove it. No hard feelings either way.
Thanks.
