path: root/arch
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authorZhang Yanfei <zhangyanfei@cn.fujitsu.com>2013-05-14 14:48:58 +0800
committerH. Peter Anvin <hpa@linux.intel.com>2013-05-28 15:41:59 -0700
commite9d0626ed43a41a3fc526d1df06122b0d4eac174 (patch)
tree691cda6bc209aac906adc70f1327001582cdc8a6 /arch
parent3979fdce77e6c2de97fa6c6f844ee76f001f4371 (diff)
x86-64, init: Fix a possible wraparound bug in switchover in head_64.S
In head_64.S, a switchover has been used to handle kernel crossing 1G, 512G boundaries. And commit 8170e6bed465b4b0c7687f93e9948aca4358a33b x86, 64bit: Use a #PF handler to materialize early mappings on demand said: During the switchover in head_64.S, before #PF handler is available, we use three pages to handle kernel crossing 1G, 512G boundaries with sharing page by playing games with page aliasing: the same page is mapped twice in the higher-level tables with appropriate wraparound. But from the switchover code, when we set up the PUD table: 114 addq $4096, %rdx 115 movq %rdi, %rax 116 shrq $PUD_SHIFT, %rax 117 andl $(PTRS_PER_PUD-1), %eax 118 movq %rdx, (4096+0)(%rbx,%rax,8) 119 movq %rdx, (4096+8)(%rbx,%rax,8) It seems line 119 has a potential bug there. For example, if the kernel is loaded at physical address 511G+1008M, that is 000000000 111111111 111111000 000000000000000000000 and the kernel _end is 512G+2M, that is 000000001 000000000 000000001 000000000000000000000 So in this example, when using the 2nd page to setup PUD (line 114~119), rax is 511. In line 118, we put rdx which is the address of the PMD page (the 3rd page) into entry 511 of the PUD table. But in line 119, the entry we calculate from (4096+8)(%rbx,%rax,8) has exceeded the PUD page. IMO, the entry in line 119 should be wraparound into entry 0 of the PUD table. The patch fixes the bug. Signed-off-by: Zhang Yanfei <zhangyanfei@cn.fujitsu.com> Link: http://lkml.kernel.org/r/5191DE5A.3020302@cn.fujitsu.com Signed-off-by: Yinghai Lu <yinghai@kernel.org> Cc: <stable@vger.kernel.org> v3.9 Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Diffstat (limited to 'arch')
1 files changed, 4 insertions, 2 deletions
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 08f7e803909..321d65ebaff 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -115,8 +115,10 @@ startup_64:
movq %rdi, %rax
shrq $PUD_SHIFT, %rax
andl $(PTRS_PER_PUD-1), %eax
- movq %rdx, (4096+0)(%rbx,%rax,8)
- movq %rdx, (4096+8)(%rbx,%rax,8)
+ movq %rdx, 4096(%rbx,%rax,8)
+ incl %eax
+ andl $(PTRS_PER_PUD-1), %eax
+ movq %rdx, 4096(%rbx,%rax,8)
addq $8192, %rbx
movq %rdi, %rax