Re: [PATCH 11/27] x86: Lock down IO port access when the kernel is locked down

[joeyli]

On Thu, Oct 19, 2017 at 03:51:56PM +0100, David Howells wrote:
> From: Matthew Garrett 
> 
> IO port access would permit users to gain access to PCI configuration
> registers, which in turn (on a lot of hardware) give access to MMIO
> register space. This would potentially permit root to trigger arbitrary
> DMA, so lock it down by default.
> 
> This also implicitly locks down the KDADDIO, KDDELIO, KDENABIO and
> KDDISABIO console ioctls.
> 
> Signed-off-by: Matthew Garrett 
> Signed-off-by: David Howells 
> Reviewed-by: Thomas Gleixner 

I have reviewed this patch. Please feel free to add:

Reviewed-by: "Lee, Chun-Yi" 

Thanks!
Joey Lee

> cc: x...@kernel.org
> ---
> 
>  arch/x86/kernel/ioport.c |6 --
>  drivers/char/mem.c   |2 ++
>  2 files changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/ioport.c b/arch/x86/kernel/ioport.c
> index 9c3cf0944bce..2c0f058651c5 100644
> --- a/arch/x86/kernel/ioport.c
> +++ b/arch/x86/kernel/ioport.c
> @@ -30,7 +30,8 @@ asmlinkage long sys_ioperm(unsigned long from, unsigned 
> long num, int turn_on)
>  
>   if ((from + num <= from) || (from + num > IO_BITMAP_BITS))
>   return -EINVAL;
> - if (turn_on && !capable(CAP_SYS_RAWIO))
> + if (turn_on && (!capable(CAP_SYS_RAWIO) ||
> + kernel_is_locked_down("ioperm")))
>   return -EPERM;
>  
>   /*
> @@ -120,7 +121,8 @@ SYSCALL_DEFINE1(iopl, unsigned int, level)
>   return -EINVAL;
>   /* Trying to gain more privileges? */
>   if (level > old) {
> - if (!capable(CAP_SYS_RAWIO))
> + if (!capable(CAP_SYS_RAWIO) ||
> + kernel_is_locked_down("iopl"))
>   return -EPERM;
>   }
>   regs->flags = (regs->flags & ~X86_EFLAGS_IOPL) |
> diff --git a/drivers/char/mem.c b/drivers/char/mem.c
> index b7c36898b689..0875b3d47773 100644
> --- a/drivers/char/mem.c
> +++ b/drivers/char/mem.c
> @@ -768,6 +768,8 @@ static loff_t memory_lseek(struct file *file, loff_t 
> offset, int orig)
>  
>  static int open_port(struct inode *inode, struct file *filp)
>  {
> + if (kernel_is_locked_down("Direct ioport access"))
> + return -EPERM;
>   return capable(CAP_SYS_RAWIO) ? 0 : -EPERM;
>  }
>  
> 
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[PATCH 11/27] x86: Lock down IO port access when the kernel is locked down

[David Howells]

From: Matthew Garrett 

IO port access would permit users to gain access to PCI configuration
registers, which in turn (on a lot of hardware) give access to MMIO
register space. This would potentially permit root to trigger arbitrary
DMA, so lock it down by default.

This also implicitly locks down the KDADDIO, KDDELIO, KDENABIO and
KDDISABIO console ioctls.

Signed-off-by: Matthew Garrett 
Signed-off-by: David Howells 
Reviewed-by: Thomas Gleixner 
cc: x...@kernel.org
---

 arch/x86/kernel/ioport.c |6 --
 drivers/char/mem.c   |2 ++
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/ioport.c b/arch/x86/kernel/ioport.c
index 9c3cf0944bce..2c0f058651c5 100644
--- a/arch/x86/kernel/ioport.c
+++ b/arch/x86/kernel/ioport.c
@@ -30,7 +30,8 @@ asmlinkage long sys_ioperm(unsigned long from, unsigned long 
num, int turn_on)
 
if ((from + num <= from) || (from + num > IO_BITMAP_BITS))
return -EINVAL;
-   if (turn_on && !capable(CAP_SYS_RAWIO))
+   if (turn_on && (!capable(CAP_SYS_RAWIO) ||
+   kernel_is_locked_down("ioperm")))
return -EPERM;
 
/*
@@ -120,7 +121,8 @@ SYSCALL_DEFINE1(iopl, unsigned int, level)
return -EINVAL;
/* Trying to gain more privileges? */
if (level > old) {
-   if (!capable(CAP_SYS_RAWIO))
+   if (!capable(CAP_SYS_RAWIO) ||
+   kernel_is_locked_down("iopl"))
return -EPERM;
}
regs->flags = (regs->flags & ~X86_EFLAGS_IOPL) |
diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index b7c36898b689..0875b3d47773 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -768,6 +768,8 @@ static loff_t memory_lseek(struct file *file, loff_t 
offset, int orig)
 
 static int open_port(struct inode *inode, struct file *filp)
 {
+   if (kernel_is_locked_down("Direct ioport access"))
+   return -EPERM;
return capable(CAP_SYS_RAWIO) ? 0 : -EPERM;
 }
 

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