From 9f0b4807a44ff81cf59421c8a86641efec586610 Mon Sep 17 00:00:00 2001 From: Johannes Berg Date: Wed, 13 Jan 2021 22:09:43 +0100 Subject: um: rework userspace stubs to not hard-code stub location The userspace stacks mostly have a stack (and in the case of the syscall stub we can just set their stack pointer) that points to the location of the stub data page already. Rework the stubs to use the stack pointer to derive the start of the data page, rather than requiring it to be hard-coded. In the clone stub, also integrate the int3 into the stack remap, since we really must not use the stack while we remap it. This prepares for putting the stub at a variable location that's not part of the normal address space of the userspace processes running inside the UML machine. Signed-off-by: Johannes Berg Signed-off-by: Richard Weinberger --- arch/x86/um/stub_32.S | 17 +++++++++++------ 1 file changed, 11 insertions(+), 6 deletions(-) (limited to 'arch/x86/um/stub_32.S') diff --git a/arch/x86/um/stub_32.S b/arch/x86/um/stub_32.S index a193e88536a9..8291899e6aaf 100644 --- a/arch/x86/um/stub_32.S +++ b/arch/x86/um/stub_32.S @@ -5,21 +5,22 @@ .globl batch_syscall_stub batch_syscall_stub: - /* load pointer to first operation */ - mov $(STUB_DATA+8), %esp - + /* %esp comes in as "top of page" */ + mov %esp, %ecx + /* %esp has pointer to first operation */ + add $8, %esp again: /* load length of additional data */ mov 0x0(%esp), %eax /* if(length == 0) : end of list */ /* write possible 0 to header */ - mov %eax, STUB_DATA+4 + mov %eax, 0x4(%ecx) cmpl $0, %eax jz done /* save current pointer */ - mov %esp, STUB_DATA+4 + mov %esp, 0x4(%ecx) /* skip additional data */ add %eax, %esp @@ -38,6 +39,10 @@ again: /* execute syscall */ int $0x80 + /* restore top of page pointer in %ecx */ + mov %esp, %ecx + andl $(~UM_KERN_PAGE_SIZE) + 1, %ecx + /* check return value */ pop %ebx cmp %ebx, %eax @@ -45,7 +50,7 @@ again: done: /* save return value */ - mov %eax, STUB_DATA + mov %eax, (%ecx) /* stop */ int3 -- cgit v1.2.3