On Tue, May 06, 2025 at 05:29:57PM -0500, Samuel Holland wrote:
That said, I wonder if set_tagged_addr_ctrl(task, 0) should succeed when Supm is not implemented, matching get_tagged_addr_ctrl(). Without Supm, we know that have_user_pmlen_7 and have_user_pmlen_16 will both be false, so pmlen == 0 is the only case where we would call envcfg_update_bits(). And we know it would be a no-op. So an alternative fix would be to return 0 below the pmlen checks:
diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c index 7c244de77180..536da9aa690e 100644 --- a/arch/riscv/kernel/process.c +++ b/arch/riscv/kernel/process.c @@ -309,6 +309,9 @@ long set_tagged_addr_ctrl(struct task_struct *task, unsigned long arg) if (!(arg & PR_TAGGED_ADDR_ENABLE)) pmlen = PMLEN_0;
- if (!riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM))
return 0;- if (mmap_write_lock_killable(mm)) return -EINTR;
But I don't know if this better matches what userspace would expect.
I'm not sure about this either. The man page says:
|If the arguments are invalid, the mode specified in arg2 is |unrecognized, or if this feature is unsupported by the kernel or disabled |via /proc/sys/abi/tagged_addr_disabled, the call fails with the error |EINVAL. | |In particular, if prctl(PR_SET_TAGGED_ADDR_CTRL, 0, 0, 0, 0) fails with |EINVAL, then all addresses passed to the kernel must be untagged.
So according to the man page, returning -EINVAL is the right thing.
But arm64 returns 0 in this case.
I would say let's follow the man page, and leave it as is.
Best regards, Nam