[PATCH] riscv: cfi: parse riscv_nousercfi before riscv_fill_hwcap()

[Guodong Xu]

ISA bitmaps don't honour riscv_nousercfi because the ISA bitmaps are
composed during setup_arch(), while riscv_nousercfi is a __setup()
parameter, and those are parsed from start_kernel() after setup_arch()
has returned.

As a consequence, the riscv_nousercfi test in riscv_cfilp_validate() and
riscv_cfiss_validate() always sees zero, and Zicfilp and Zicfiss stay in
the ISA bitmaps even when user CFI is disabled on the kernel command
line.

Register the option with early_param() instead. The handler now returns
0 on success, as early_param() expects. Also in this patch, reject a
bare "riscv_nousercfi" without a value, which early_param() passes in as
a NULL string.

Fixes: c9b859c4d8f5 ("riscv: add kernel command line option to opt out of user CFI")
Signed-off-by: Guodong Xu <guodong.xu at oss.qualcomm.com>
---
Tested on QEMU (rva23s64 with zicfilp and zicfiss, 4 harts).

qemu-system-riscv64 -M virt -smp 4 -cpu rva23s64,zicfilp=true,zicfiss=true

Without the patch, with 'riscv_nousercfi=all', cpuinfo and hwprobe keep
reporting the disabled extensions.
---
 Documentation/admin-guide/kernel-parameters.txt | 2 +-
 arch/riscv/kernel/usercfi.c                     | 7 +++++--
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 0b3c140babd9..b8d9db39497e 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -6714,7 +6714,7 @@ Kernel parameters
 			replacement properties are not found. See the Kconfig
 			entry for RISCV_ISA_FALLBACK.
 
-	riscv_nousercfi=
+	riscv_nousercfi=	[RISCV,EARLY]
 		all	Disable user CFI ABI to userspace even if cpu extension
 			are available.
 		bcfi	Disable user backward CFI ABI to userspace even if
diff --git a/arch/riscv/kernel/usercfi.c b/arch/riscv/kernel/usercfi.c
index 86141e5bab82..a3446d706cf1 100644
--- a/arch/riscv/kernel/usercfi.c
+++ b/arch/riscv/kernel/usercfi.c
@@ -508,6 +508,9 @@ bool is_user_lpad_enabled(void)
 
 static int __init setup_global_riscv_enable(char *str)
 {
+	if (!str)
+		return -EINVAL;
+
 	if (strcmp(str, "all") == 0)
 		riscv_nousercfi = CMDLINE_DISABLE_RISCV_USERCFI;
 
@@ -522,7 +525,7 @@ static int __init setup_global_riscv_enable(char *str)
 			str_disabled_enabled(riscv_nousercfi & CMDLINE_DISABLE_RISCV_USERCFI_BCFI),
 			str_disabled_enabled(riscv_nousercfi & CMDLINE_DISABLE_RISCV_USERCFI_FCFI));
 
-	return 1;
+	return 0;
 }
 
-__setup("riscv_nousercfi=", setup_global_riscv_enable);
+early_param("riscv_nousercfi", setup_global_riscv_enable);

---
base-commit: 6628e7d4c6b25c8d18f1345e3a20d21829aae7e4
change-id: 20261108-nousercfi-early-param-c48f7d54c168

Best regards,
--  
Guodong Xu <guodong.xu at oss.qualcomm.com>