From 8b1d72395635af45410b66cc4c4ab37a12c4a831 Mon Sep 17 00:00:00 2001 From: Helge Deller Date: Sat, 20 Jan 2024 15:29:27 +0100 Subject: parisc: Fix random data corruption from exception handler The current exception handler implementation, which assists when accessing user space memory, may exhibit random data corruption if the compiler decides to use a different register than the specified register %r29 (defined in ASM_EXCEPTIONTABLE_REG) for the error code. If the compiler choose another register, the fault handler will nevertheless store -EFAULT into %r29 and thus trash whatever this register is used for. Looking at the assembly I found that this happens sometimes in emulate_ldd(). To solve the issue, the easiest solution would be if it somehow is possible to tell the fault handler which register is used to hold the error code. Using %0 or %1 in the inline assembly is not posssible as it will show up as e.g. %r29 (with the "%r" prefix), which the GNU assembler can not convert to an integer. This patch takes another, better and more flexible approach: We extend the __ex_table (which is out of the execution path) by one 32-word. In this word we tell the compiler to insert the assembler instruction "or %r0,%r0,%reg", where %reg references the register which the compiler choosed for the error return code. In case of an access failure, the fault handler finds the __ex_table entry and can examine the opcode. The used register is encoded in the lowest 5 bits, and the fault handler can then store -EFAULT into this register. Since we extend the __ex_table to 3 words we can't use the BUILDTIME_TABLE_SORT config option any longer. Signed-off-by: Helge Deller Cc: # v6.0+ --- arch/parisc/Kconfig | 1 - 1 file changed, 1 deletion(-) (limited to 'arch/parisc/Kconfig') diff --git a/arch/parisc/Kconfig b/arch/parisc/Kconfig index d14ccc948a29..5c845e8d59d9 100644 --- a/arch/parisc/Kconfig +++ b/arch/parisc/Kconfig @@ -25,7 +25,6 @@ config PARISC select RTC_DRV_GENERIC select INIT_ALL_POSSIBLE select BUG - select BUILDTIME_TABLE_SORT select HAVE_KERNEL_UNCOMPRESSED select HAVE_PCI select HAVE_PERF_EVENTS -- cgit v1.2.3