arm64/signal: Silence sparse warning storing GCSPR_EL0

We are seeing a sparse warning in gcs_restore_signal():

  arch/arm64/kernel/signal.c:1054:9: sparse: sparse: cast removes address space '__user' of expression

when storing the final GCSPR_EL0 value back into the register, caused by
the fact that write_sysreg_s() casts the value it writes to a u64 which
sparse sees as discarding the __userness of the pointer.

Avoid this by treating the address as an integer, casting to a pointer only
when using it to write to userspace.

While we're at it also inline gcs_signal_cap_valid() into it's one user
and make equivalent updates to gcs_signal_entry().

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202412082005.OBJ0BbWs-lkp@intel.com/
Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20241214-arm64-gcs-signal-sparse-v3-1-5e8d18fffc0c@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
index 37e24f1bd2279f541c38e4c84a030da7877691bd..99ea26d400ffeb2f00eb03f4f428be3b32cf8ab0 100644 (file)
--- a/arch/arm64/kernel/signal.c
+++ b/arch/arm64/kernel/signal.c
@@ -36,15 +36,8 @@
 #include <asm/traps.h>
 #include <asm/vdso.h>
 
-#ifdef CONFIG_ARM64_GCS
 #define GCS_SIGNAL_CAP(addr) (((unsigned long)addr) & GCS_CAP_ADDR_MASK)
 
-static bool gcs_signal_cap_valid(u64 addr, u64 val)
-{
-       return val == GCS_SIGNAL_CAP(addr);
-}
-#endif
-
 /*
  * Do a signal return; undo the signal stack. These are aligned to 128-bit.
  */
@@ -1062,8 +1055,7 @@ static int restore_sigframe(struct pt_regs *regs,
 #ifdef CONFIG_ARM64_GCS
 static int gcs_restore_signal(void)
 {
-       unsigned long __user *gcspr_el0;
-       u64 cap;
+       u64 gcspr_el0, cap;
        int ret;
 
        if (!system_supports_gcs())
@@ -1072,7 +1064,7 @@ static int gcs_restore_signal(void)
        if (!(current->thread.gcs_el0_mode & PR_SHADOW_STACK_ENABLE))
                return 0;
 
-       gcspr_el0 = (unsigned long __user *)read_sysreg_s(SYS_GCSPR_EL0);
+       gcspr_el0 = read_sysreg_s(SYS_GCSPR_EL0);
 
        /*
         * Ensure that any changes to the GCS done via GCS operations
@@ -1087,22 +1079,23 @@ static int gcs_restore_signal(void)
         * then faults will be generated on GCS operations - the main
         * concern is to protect GCS pages.
         */
-       ret = copy_from_user(&cap, gcspr_el0, sizeof(cap));
+       ret = copy_from_user(&cap, (unsigned long __user *)gcspr_el0,
+                            sizeof(cap));
        if (ret)
                return -EFAULT;
 
        /*
         * Check that the cap is the actual GCS before replacing it.
         */
-       if (!gcs_signal_cap_valid((u64)gcspr_el0, cap))
+       if (cap != GCS_SIGNAL_CAP(gcspr_el0))
                return -EINVAL;
 
        /* Invalidate the token to prevent reuse */
-       put_user_gcs(0, (__user void*)gcspr_el0, &ret);
+       put_user_gcs(0, (unsigned long __user *)gcspr_el0, &ret);
        if (ret != 0)
                return -EFAULT;
 
-       write_sysreg_s(gcspr_el0 + 1, SYS_GCSPR_EL0);
+       write_sysreg_s(gcspr_el0 + 8, SYS_GCSPR_EL0);
 
        return 0;
 }
@@ -1421,7 +1414,7 @@ static int get_sigframe(struct rt_sigframe_user_layout *user,
 
 static int gcs_signal_entry(__sigrestore_t sigtramp, struct ksignal *ksig)
 {
-       unsigned long __user *gcspr_el0;
+       u64 gcspr_el0;
        int ret = 0;
 
        if (!system_supports_gcs())
@@ -1434,18 +1427,20 @@ static int gcs_signal_entry(__sigrestore_t sigtramp, struct ksignal *ksig)
         * We are entering a signal handler, current register state is
         * active.
         */
-       gcspr_el0 = (unsigned long __user *)read_sysreg_s(SYS_GCSPR_EL0);
+       gcspr_el0 = read_sysreg_s(SYS_GCSPR_EL0);
 
        /*
         * Push a cap and the GCS entry for the trampoline onto the GCS.
         */
-       put_user_gcs((unsigned long)sigtramp, gcspr_el0 - 2, &ret);
-       put_user_gcs(GCS_SIGNAL_CAP(gcspr_el0 - 1), gcspr_el0 - 1, &ret);
+       put_user_gcs((unsigned long)sigtramp,
+                    (unsigned long __user *)(gcspr_el0 - 16), &ret);
+       put_user_gcs(GCS_SIGNAL_CAP(gcspr_el0 - 8),
+                    (unsigned long __user *)(gcspr_el0 - 8), &ret);
        if (ret != 0)
                return ret;
 
-       gcspr_el0 -= 2;
-       write_sysreg_s((unsigned long)gcspr_el0, SYS_GCSPR_EL0);
+       gcspr_el0 -= 16;
+       write_sysreg_s(gcspr_el0, SYS_GCSPR_EL0);
 
        return 0;
 }