[PATCH] Revert "riscv: Reset pmm when PR_TAGGED_ADDR_ENABLE is not set"

[PATCH] Revert "riscv: Reset pmm when PR_TAGGED_ADDR_ENABLE is not set"

[Samuel Holland]

This reverts commit 3033b2b1e3949274f33a140e2a97571b5a307298.

The reverted patch is userspace-visible behavior change, not a bug fix.
The two variables here (pmm and pmlen) control two independent features:
pmm is the _hardware_ pointer masking mode that applies while executing
in userspace. pmlen is the shift amount that the _kernel_ uses when
untagging addresses; PMLEN_0 means no untagging occurs, so the kernel
does not accept tagged addresses in syscall arguments.

It is valid (as documented and tested by the self test) to enable
pointer masking without enabling the tagged address ABI. This separation
is necessary to allow userspace to create an execution environment
similar to what the kernel supports on arm64 by default, where TBI is
enabled but the tagged address ABI is not. (On arm64, there is no
equivalent to PR_PMLEN_MASK because TBI is always enabled.)

Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
---

 arch/riscv/kernel/process.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
index b2df7f72241a5..7cc5a6a5c0206 100644
--- a/arch/riscv/kernel/process.c
+++ b/arch/riscv/kernel/process.c
@@ -349,10 +349,8 @@ long set_tagged_addr_ctrl(struct task_struct *task, unsigned long arg)
 	if (arg & PR_TAGGED_ADDR_ENABLE && (tagged_addr_disabled || !pmlen))
 		return -EINVAL;
 
-	if (!(arg & PR_TAGGED_ADDR_ENABLE)) {
+	if (!(arg & PR_TAGGED_ADDR_ENABLE))
 		pmlen = PMLEN_0;
-		pmm = ENVCFG_PMM_PMLEN_0;
-	}
 
 	if (mmap_write_lock_killable(mm))
 		return -EINTR;
-- 
2.52.0

base-commit: a4ff2be345d0abc943da8dd8da98151843b750dc
branch: up/pointer-masking-fix

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Re: [PATCH] Revert "riscv: Reset pmm when PR_TAGGED_ADDR_ENABLE is not set"

[Paul Walmsley]

On Wed, 19 Aug 2026, Samuel Holland wrote:

> This reverts commit 3033b2b1e3949274f33a140e2a97571b5a307298.
> 
> The reverted patch is userspace-visible behavior change, not a bug fix.
> The two variables here (pmm and pmlen) control two independent features:
> pmm is the _hardware_ pointer masking mode that applies while executing
> in userspace. pmlen is the shift amount that the _kernel_ uses when
> untagging addresses; PMLEN_0 means no untagging occurs, so the kernel
> does not accept tagged addresses in syscall arguments.
> 
> It is valid (as documented and tested by the self test) to enable
> pointer masking without enabling the tagged address ABI. This separation
> is necessary to allow userspace to create an execution environment
> similar to what the kernel supports on arm64 by default, where TBI is
> enabled but the tagged address ABI is not. (On arm64, there is no
> equivalent to PR_PMLEN_MASK because TBI is always enabled.)
> 
> Signed-off-by: Samuel Holland <samuel.holland@sifive.com>

Thanks, queued for v7.3-rc with a Fixes: tag and cc: stable.


- Paul

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