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arm64/signal: Silence sparse warning storing GCSPR_EL0

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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>
This commit is contained in:
Mark Brown 2024-12-14 02:12:06 +00:00 committed by Catalin Marinas
parent ce03573a19
commit 926e862058
1 changed files with 15 additions and 20 deletions
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35
arch/arm64/kernel/signal.c
View File

@ -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;
}