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authorRussell King <rmk+kernel@armlinux.org.uk>2020-05-03 13:24:07 +0100
committerRussell King <rmk+kernel@armlinux.org.uk>2020-05-03 17:30:27 +0100
commit71f8af1110101facfad68989ff91f88f8e2c3e22 (patch)
tree86f5eee6c2f3d5cbd5573b578fe512567dddaa28
parent8ede890b0bcebe8c760aacfe20e934d98c3dc6aa (diff)
ARM: uaccess: fix DACR mismatch with nested exceptionsuaccess
Tomas Paukrt reports that his SAM9X60 based system (ARM926, ARMv5TJ) fails to fix up alignment faults, eventually resulting in a kernel oops. The problem occurs when using CONFIG_CPU_USE_DOMAINS with commit e6978e4bf181 ("ARM: save and reset the address limit when entering an exception"). This is because the address limit is set back to TASK_SIZE on exception entry, and, although it is restored on exception exit, the domain register is not. Hence, this sequence can occur: interrupt pt_regs->addr_limit = addr_limit // USER_DS addr_limit = USER_DS alignment exception __probe_kernel_read() old_fs = get_fs() // USER_DS set_fs(KERNEL_DS) addr_limit = KERNEL_DS dacr.kernel = DOMAIN_MANAGER interrupt pt_regs->addr_limit = addr_limit // KERNEL_DS addr_limit = USER_DS alignment exception __probe_kernel_read() old_fs = get_fs() // USER_DS set_fs(KERNEL_DS) addr_limit = KERNEL_DS dacr.kernel = DOMAIN_MANAGER ... set_fs(old_fs) addr_limit = USER_DS dacr.kernel = DOMAIN_CLIENT ... addr_limit = pt_regs->addr_limit // KERNEL_DS interrupt returns At this point, addr_limit is correctly restored to KERNEL_DS for __probe_kernel_read() to continue execution, but dacr.kernel is not, it has been reset by the set_fs(old_fs) to DOMAIN_CLIENT. This would not have happened prior to the mentioned commit, because addr_limit would remain KERNEL_DS, so get_fs() would have returned KERNEL_DS, and so would correctly nest. This commit fixes the problem by also saving the DACR on exception entry if either CONFIG_CPU_SW_DOMAIN_PAN or CONFIG_CPU_USE_DOMAINS are enabled, and resetting the DACR appropriately on exception entry to match addr_limit and PAN settings. Fixes: e6978e4bf181 ("ARM: save and reset the address limit when entering an exception") Reported-by: Tomas Paukrt <tomas.paukrt@advantech.cz> Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
-rw-r--r--arch/arm/include/asm/uaccess-asm.h25
1 files changed, 20 insertions, 5 deletions
diff --git a/arch/arm/include/asm/uaccess-asm.h b/arch/arm/include/asm/uaccess-asm.h
index e46468b91eaa..907571fd05c6 100644
--- a/arch/arm/include/asm/uaccess-asm.h
+++ b/arch/arm/include/asm/uaccess-asm.h
@@ -67,15 +67,21 @@
#endif
.endm
-#ifdef CONFIG_CPU_SW_DOMAIN_PAN
+#if defined(CONFIG_CPU_SW_DOMAIN_PAN) || defined(CONFIG_CPU_USE_DOMAINS)
#define DACR(x...) x
#else
#define DACR(x...)
#endif
/*
- * Save the address limit on entry to a privileged exception and
- * if using PAN, save and disable usermode access.
+ * Save the address limit on entry to a privileged exception.
+ *
+ * If we are using the DACR for kernel access by the user accessors
+ * (CONFIG_CPU_USE_DOMAINS=y), always reset the DACR kernel domain
+ * back to client mode, whether or not \disable is set.
+ *
+ * If we are using SW PAN, set the DACR user domain to no access
+ * if \disable is set.
*/
.macro uaccess_entry, tsk, tmp0, tmp1, tmp2, disable
ldr \tmp1, [\tsk, #TI_ADDR_LIMIT]
@@ -84,8 +90,17 @@
DACR( mrc p15, 0, \tmp0, c3, c0, 0)
DACR( str \tmp0, [sp, #SVC_DACR])
str \tmp1, [sp, #SVC_ADDR_LIMIT]
- .if \disable
- uaccess_disable \tmp0
+ .if \disable && IS_ENABLED(CONFIG_CPU_SW_DOMAIN_PAN)
+ /* kernel=client, user=no access */
+ mov \tmp2, #DACR_UACCESS_DISABLE
+ mcr p15, 0, \tmp2, c3, c0, 0
+ instr_sync
+ .elseif IS_ENABLED(CONFIG_CPU_USE_DOMAINS)
+ /* kernel=client */
+ bic \tmp2, \tmp0, #domain_mask(DOMAIN_KERNEL)
+ orr \tmp2, \tmp2, #domain_val(DOMAIN_KERNEL, DOMAIN_CLIENT)
+ mcr p15, 0, \tmp2, c3, c0, 0
+ instr_sync
.endif
.endm