From: Will Deacon Date: Thu, 15 Oct 2015 12:55:53 +0000 (+0100) Subject: arm64: compat: fix stxr failure case in SWP emulation X-Git-Tag: v4.2.6~7 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=5ce538743aafc5aef4775ae6e8aed57e23d5e40b;p=thirdparty%2Fkernel%2Fstable.git arm64: compat: fix stxr failure case in SWP emulation commit 589cb22bbedacf325951014c07a35a2b01ca57f6 upstream. If the STXR instruction fails in the SWP emulation code, we leave *data overwritten with the loaded value, therefore corrupting the data written by a subsequent, successful attempt. This patch re-jigs the code so that we only write back to *data once we know that the update has happened. Fixes: bd35a4adc413 ("arm64: Port SWP/SWPB emulation support from arm") Reported-by: Shengjiu Wang Reported-by: Vladimir Murzin Signed-off-by: Will Deacon Signed-off-by: Greg Kroah-Hartman --- diff --git a/arch/arm64/kernel/armv8_deprecated.c b/arch/arm64/kernel/armv8_deprecated.c index 7922c2e710cad..7ac3920b1356a 100644 --- a/arch/arm64/kernel/armv8_deprecated.c +++ b/arch/arm64/kernel/armv8_deprecated.c @@ -279,22 +279,24 @@ static void register_insn_emulation_sysctl(struct ctl_table *table) */ #define __user_swpX_asm(data, addr, res, temp, B) \ __asm__ __volatile__( \ - " mov %w2, %w1\n" \ - "0: ldxr"B" %w1, [%3]\n" \ - "1: stxr"B" %w0, %w2, [%3]\n" \ + "0: ldxr"B" %w2, [%3]\n" \ + "1: stxr"B" %w0, %w1, [%3]\n" \ " cbz %w0, 2f\n" \ " mov %w0, %w4\n" \ + " b 3f\n" \ "2:\n" \ + " mov %w1, %w2\n" \ + "3:\n" \ " .pushsection .fixup,\"ax\"\n" \ " .align 2\n" \ - "3: mov %w0, %w5\n" \ - " b 2b\n" \ + "4: mov %w0, %w5\n" \ + " b 3b\n" \ " .popsection" \ " .pushsection __ex_table,\"a\"\n" \ " .align 3\n" \ - " .quad 0b, 3b\n" \ - " .quad 1b, 3b\n" \ - " .popsection" \ + " .quad 0b, 4b\n" \ + " .quad 1b, 4b\n" \ + " .popsection\n" \ : "=&r" (res), "+r" (data), "=&r" (temp) \ : "r" (addr), "i" (-EAGAIN), "i" (-EFAULT) \ : "memory")