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https://github.com/AuxXxilium/linux_dsm_epyc7002.git
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abafe5d9b0
When invoking syscall handlers on sh32, the saved userspace registers
are at the top of the stack. This seems to have been intentional, as it
is an easy way to pass r0, r1, ... to the handler as parameters 5, 6,
...
It causes problems, however, because the compiler is allowed to generate
code for a function which clobbers that function's own parameters. For
example, gcc generates the following code for clone:
<SyS_clone>:
mov.l 8c020714 <SyS_clone+0xc>,r1 ! 8c020540 <do_fork>
mov.l r7,@r15
mov r6,r7
jmp @r1
mov #0,r6
nop
.word 0x0540
.word 0x8c02
The `mov.l r7,@r15` clobbers the saved value of r0 passed from
userspace. For most system calls, this might not be a problem, because
we'll be overwriting r0 with the return value anyway. But in the case
of clone, copy_thread will need the original value of r0 if the
CLONE_SETTLS flag was specified.
The first patch in this series fixes this issue for system calls by
pushing to the stack and extra copy of r0-r2 before invoking the
handler. We discard this copy before restoring the userspace registers,
so it is not a problem if they are clobbered.
Exception handlers also receive the userspace register values in a
similar manner, and may hit the same problem. The second patch removes
the do_fpu_error handler, which looks susceptible to this problem and
which, as far as I can tell, has not been used in some time. The third
patch addresses other exception handlers.
This patch (of 3):
The userspace registers are stored at the top of the stack when the
syscall handler is invoked, which allows r0-r2 to act as parameters 5-7.
Parameters passed on the stack may be clobbered by the syscall handler.
The solution is to push an extra copy of the registers which might be
used as syscall parameters to the stack, so that the authoritative set
of saved register values does not get clobbered.
A few system call handlers are also updated to get the userspace
registers using current_pt_regs() instead of from the stack.
Signed-off-by: Bobby Bingham <koorogi@koorogi.info>
Cc: Paul Mundt <paul.mundt@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
60 lines
1.4 KiB
C
60 lines
1.4 KiB
C
#include <linux/errno.h>
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#include <linux/sched.h>
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#include <linux/mm.h>
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#include <linux/smp.h>
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#include <linux/sem.h>
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#include <linux/msg.h>
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#include <linux/shm.h>
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#include <linux/stat.h>
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#include <linux/syscalls.h>
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#include <linux/mman.h>
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#include <linux/file.h>
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#include <linux/module.h>
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#include <linux/fs.h>
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#include <linux/ipc.h>
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#include <asm/cacheflush.h>
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#include <asm/uaccess.h>
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#include <asm/unistd.h>
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#include <asm/syscalls.h>
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/*
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* sys_pipe() is the normal C calling standard for creating
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* a pipe. It's not the way Unix traditionally does this, though.
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*/
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asmlinkage int sys_sh_pipe(void)
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{
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int fd[2];
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int error;
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error = do_pipe_flags(fd, 0);
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if (!error) {
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current_pt_regs()->regs[1] = fd[1];
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return fd[0];
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}
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return error;
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}
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asmlinkage ssize_t sys_pread_wrapper(unsigned int fd, char __user *buf,
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size_t count, long dummy, loff_t pos)
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{
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return sys_pread64(fd, buf, count, pos);
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}
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asmlinkage ssize_t sys_pwrite_wrapper(unsigned int fd, const char __user *buf,
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size_t count, long dummy, loff_t pos)
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{
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return sys_pwrite64(fd, buf, count, pos);
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}
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asmlinkage int sys_fadvise64_64_wrapper(int fd, u32 offset0, u32 offset1,
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u32 len0, u32 len1, int advice)
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{
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#ifdef __LITTLE_ENDIAN__
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return sys_fadvise64_64(fd, (u64)offset1 << 32 | offset0,
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(u64)len1 << 32 | len0, advice);
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#else
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return sys_fadvise64_64(fd, (u64)offset0 << 32 | offset1,
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(u64)len0 << 32 | len1, advice);
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#endif
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}
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