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vsyscall detection code uses direct call to the beginning of
the vsyscall page:
asm ("call %P0" :: "i" (0xffffffffff600000))
It generates "call rel32" instruction but it is not relocated if binary
is PIE, so binary segfaults into random userspace address and vsyscall
page status is detected incorrectly.
Do more direct:
asm ("call *%rax")
which doesn't do need any relocaltions.
Mark g_vsyscall as volatile for a good measure, I didn't find instruction
setting it to 0. Now the code is obviously correct:
xor eax, eax
mov rdi, rbp
mov rsi, rbp
mov DWORD PTR [rip+0x2d15], eax # g_vsyscall = 0
mov rax, 0xffffffffff600000
call rax
mov DWORD PTR [rip+0x2d02], 1 # g_vsyscall = 1
mov eax, DWORD PTR ds:0xffffffffff600000
mov DWORD PTR [rip+0x2cf1], 2 # g_vsyscall = 2
mov edi, [rip+0x2ceb] # exit(g_vsyscall)
call exit
Note: fixed proc-empty-vm test oopses 5.19.0-28-generic kernel
but this is separate story.
Link: https://lkml.kernel.org/r/Y7h2xvzKLg36DSq8@p183
Fixes: 5bc73bb345 ("proc: test how it holds up with mapping'less process")
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Reported-by: Mirsad Goran Todorovac <mirsad.todorovac@alu.unizg.hr>
Tested-by: Mirsad Goran Todorovac <mirsad.todorovac@alu.unizg.hr>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
5316a017d0