Commit 926e8620 authored by Mark Brown's avatar Mark Brown Committed by Catalin Marinas
Browse files

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: default avatarkernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202412082005.OBJ0BbWs-lkp@intel.com/


Signed-off-by: default avatarMark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20241214-arm64-gcs-signal-sparse-v3-1-5e8d18fffc0c@kernel.org


Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent ce03573a

arch/arm64/kernel/signal.c

+15 −20
Original line number Diff line number Diff line
@@ -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;

}