[PATCH 2.4.31 6/9] gcc4: fix x86_64 sys_iopl() bug

From: Mikael Pettersson (mikpe_at_csd.uu.se)
Date: 06/12/05

  • Next message: Mikael Pettersson: "[PATCH 2.4.31 7/9] gcc4: fix const function warnings" 
    Date:	Sun, 12 Jun 2005 13:20:35 +0200 (MEST)
To: marcelo.tosatti@cyclades.com

    On x86_64 sys_iopl() becomes a no-op when compiled with gcc4.
    This breaks the X server, causing its PCI probing to fail.

    This is caused by a bug. sys_iopl() receives a struct pt_regs as
    a formal parameter, and updates it expecting those updates to
    remain when it returns. This is incorrect as the calling convention
    rules say that a function's formal parameters are initialised
    copies that disappear when the function returns.

    The fix (backport from 2.6) is to pass the pt_regs by reference.

    Signed-off-by: Mikael Pettersson <mikpe@csd.uu.se>

     arch/x86_64/ia32/ia32entry.S | 11 ++++++++++-
     arch/x86_64/kernel/entry.S | 11 ++++++++++-
     arch/x86_64/kernel/ioport.c | 6 +++---
     3 files changed, 23 insertions(+), 5 deletions(-)

    diff -rupN linux-2.4.31/arch/x86_64/ia32/ia32entry.S linux-2.4.31.gcc4-x86_64-iopl-bug/arch/x86_64/ia32/ia32entry.S
    --- linux-2.4.31/arch/x86_64/ia32/ia32entry.S 2005-01-19 18:00:53.000000000 +0100
    +++ linux-2.4.31.gcc4-x86_64-iopl-bug/arch/x86_64/ia32/ia32entry.S 2005-06-12 11:46:56.000000000 +0200
    @@ -113,9 +113,18 @@ quiet_ni_syscall:
             PTREGSCALL stub32_fork, sys32_fork
             PTREGSCALL stub32_clone, sys32_clone
             PTREGSCALL stub32_vfork, sys32_vfork
    - PTREGSCALL stub32_iopl, sys_iopl
             PTREGSCALL stub32_rt_sigsuspend, sys_rt_sigsuspend
     
    + .macro PTREGSCALL3 label, func, arg
    + .globl \label
    +\label:
    + leaq \func(%rip),%rax
    + leaq -ARGOFFSET+8(%rsp),\arg /* 8 for return address */
    + jmp ia32_ptregs_common
    + .endm
    +
    + PTREGSCALL3 stub32_iopl, sys_iopl, %rsi
    +
     ENTRY(ia32_ptregs_common)
             popq %r11
             SAVE_REST
    diff -rupN linux-2.4.31/arch/x86_64/kernel/entry.S linux-2.4.31.gcc4-x86_64-iopl-bug/arch/x86_64/kernel/entry.S
    --- linux-2.4.31/arch/x86_64/kernel/entry.S 2003-11-29 00:28:11.000000000 +0100
    +++ linux-2.4.31.gcc4-x86_64-iopl-bug/arch/x86_64/kernel/entry.S 2005-06-12 11:46:56.000000000 +0200
    @@ -249,7 +249,16 @@ intret_signal_test:
             PTREGSCALL stub_vfork, sys_vfork
             PTREGSCALL stub_rt_sigsuspend, sys_rt_sigsuspend
             PTREGSCALL stub_sigaltstack, sys_sigaltstack
    - PTREGSCALL stub_iopl, sys_iopl
    +
    + .macro PTREGSCALL3 label,func,arg
    + .globl \label
    +\label:
    + leaq \func(%rip),%rax
    + leaq -ARGOFFSET+8(%rsp),\arg /* 8 for return address */
    + jmp ptregscall_common
    + .endm
    +
    + PTREGSCALL3 stub_iopl, sys_iopl, %rsi
     
     ENTRY(ptregscall_common)
             popq %r11
    diff -rupN linux-2.4.31/arch/x86_64/kernel/ioport.c linux-2.4.31.gcc4-x86_64-iopl-bug/arch/x86_64/kernel/ioport.c
    --- linux-2.4.31/arch/x86_64/kernel/ioport.c 2003-11-29 00:28:11.000000000 +0100
    +++ linux-2.4.31.gcc4-x86_64-iopl-bug/arch/x86_64/kernel/ioport.c 2005-06-12 11:46:56.000000000 +0200
    @@ -81,9 +81,9 @@ asmlinkage long sys_ioperm(unsigned long
      * code.
      */
     
    -asmlinkage long sys_iopl(unsigned int level, struct pt_regs regs)
    +asmlinkage long sys_iopl(unsigned int level, struct pt_regs *regs)
     {
    - unsigned int old = (regs.eflags >> 12) & 3;
    + unsigned int old = (regs->eflags >> 12) & 3;
     
             if (level > 3)
                     return -EINVAL;
    @@ -92,6 +92,6 @@ asmlinkage long sys_iopl(unsigned int le
                     if (!capable(CAP_SYS_RAWIO))
                             return -EPERM;
             }
    - regs.eflags = (regs.eflags & 0xffffffffffffcfff) | (level << 12);
    + regs->eflags = (regs->eflags &~ 0x3000UL) | (level << 12);
             return 0;
     }
    -
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