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Date: Mon, 14 Jan 2013 12:16:19 -0700
From: Bjorn Helgaas <bhelgaas@...gle.com>
To: Cong Ding <dinggnu@...il.com>
Cc: Tony Luck <tony.luck@...el.com>, Fenghua Yu <fenghua.yu@...el.com>,
linux-altix@....com, linux-ia64@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ia64: sn/pci/pcibr/pcibr_reg.c: check null pointer dereference
[-cc jes@....com (stale)]
On Mon, Jan 14, 2013 at 11:47 AM, Cong Ding <dinggnu@...il.com> wrote:
> On Mon, Jan 14, 2013 at 11:19:15AM -0700, Bjorn Helgaas wrote:
>> On Mon, Jan 14, 2013 at 10:53 AM, Cong Ding <dinggnu@...il.com> wrote:
>> > we should ensure the pointer is not null before the first use, rather than
>> > after it.
>>
>> These changes look technically correct, but the whole pcibr_reg.c file
>> is ridiculously defensive programming.
>>
>> For example, the first two hunks are for pcireg_control_bit_clr() and
>> pcireg_control_bit_set(). These functions are called only from
>> pcibr_bus_fixup(), and it's impossible for it to pass a null pointer.
>> It would be better to just remove the null pointer checks completely.
>>
>> The panics in pcibr_reg.c are dubious, too. That sort of check
>> belongs higher up, e.g., in pcibr_bus_fixup() where we set up
>> pcibus_info->pbi_buscommon.bs_base in the first place.
>>
> Thanks Bjorn, so do you think a patch like the following would be better?
Well, you have to do the rest of the analysis. I didn't look at *all*
the functions in pcibr_reg.c, and I know some of them are called from
places other than pcibr_bus_fixup(). I suspect the same idea applies
to all, but you need to verify that and update the commit log
accordingly.
> From 5c4798565320b2eeda23b68fdf950322f4ea66ff Mon Sep 17 00:00:00 2001
> From: Cong Ding <dinggnu@...il.com>
> Date: Mon, 14 Jan 2013 18:41:24 +0000
> Subject: [PATCH] ia64: sn/pci/pcibr/pcibr_reg.c: remove unnecessary null pointer check
>
> These functions are called only from pcibr_bus_fixup(), and it's impossible
> for it to pass a null pointer. And these pointers are used before the checks.
>
> Signed-off-by: Cong Ding <dinggnu@...il.com>
> ---
> arch/ia64/sn/pci/pcibr/pcibr_reg.c | 271 ++++++++++++++++--------------------
> 1 files changed, 120 insertions(+), 151 deletions(-)
>
> diff --git a/arch/ia64/sn/pci/pcibr/pcibr_reg.c b/arch/ia64/sn/pci/pcibr/pcibr_reg.c
> index 8b8bbd5..ae16be3c 100644
> --- a/arch/ia64/sn/pci/pcibr/pcibr_reg.c
> +++ b/arch/ia64/sn/pci/pcibr/pcibr_reg.c
> @@ -27,19 +27,16 @@ void pcireg_control_bit_clr(struct pcibus_info *pcibus_info, u64 bits)
> {
> union br_ptr __iomem *ptr = (union br_ptr __iomem *)pcibus_info->pbi_buscommon.bs_base;
>
> - if (pcibus_info) {
> - switch (pcibus_info->pbi_bridge_type) {
> - case PCIBR_BRIDGETYPE_TIOCP:
> - __sn_clrq_relaxed(&ptr->tio.cp_control, bits);
> - break;
> - case PCIBR_BRIDGETYPE_PIC:
> - __sn_clrq_relaxed(&ptr->pic.p_wid_control, bits);
> - break;
> - default:
> - panic
> - ("pcireg_control_bit_clr: unknown bridgetype bridge 0x%p",
> - ptr);
> - }
> + switch (pcibus_info->pbi_bridge_type) {
> + case PCIBR_BRIDGETYPE_TIOCP:
> + __sn_clrq_relaxed(&ptr->tio.cp_control, bits);
> + break;
> + case PCIBR_BRIDGETYPE_PIC:
> + __sn_clrq_relaxed(&ptr->pic.p_wid_control, bits);
> + break;
> + default:
> + panic("pcireg_control_bit_clr: unknown bridgetype bridge 0x%p",
> + ptr);
> }
> }
>
> @@ -47,19 +44,16 @@ void pcireg_control_bit_set(struct pcibus_info *pcibus_info, u64 bits)
> {
> union br_ptr __iomem *ptr = (union br_ptr __iomem *)pcibus_info->pbi_buscommon.bs_base;
>
> - if (pcibus_info) {
> - switch (pcibus_info->pbi_bridge_type) {
> - case PCIBR_BRIDGETYPE_TIOCP:
> - __sn_setq_relaxed(&ptr->tio.cp_control, bits);
> - break;
> - case PCIBR_BRIDGETYPE_PIC:
> - __sn_setq_relaxed(&ptr->pic.p_wid_control, bits);
> - break;
> - default:
> - panic
> - ("pcireg_control_bit_set: unknown bridgetype bridge 0x%p",
> - ptr);
> - }
> + switch (pcibus_info->pbi_bridge_type) {
> + case PCIBR_BRIDGETYPE_TIOCP:
> + __sn_setq_relaxed(&ptr->tio.cp_control, bits);
> + break;
> + case PCIBR_BRIDGETYPE_PIC:
> + __sn_setq_relaxed(&ptr->pic.p_wid_control, bits);
> + break;
> + default:
> + panic("pcireg_control_bit_set: unknown bridgetype bridge 0x%p",
> + ptr);
> }
> }
>
> @@ -71,19 +65,16 @@ u64 pcireg_tflush_get(struct pcibus_info *pcibus_info)
> union br_ptr __iomem *ptr = (union br_ptr __iomem *)pcibus_info->pbi_buscommon.bs_base;
> u64 ret = 0;
>
> - if (pcibus_info) {
> - switch (pcibus_info->pbi_bridge_type) {
> - case PCIBR_BRIDGETYPE_TIOCP:
> - ret = __sn_readq_relaxed(&ptr->tio.cp_tflush);
> - break;
> - case PCIBR_BRIDGETYPE_PIC:
> - ret = __sn_readq_relaxed(&ptr->pic.p_wid_tflush);
> - break;
> - default:
> - panic
> - ("pcireg_tflush_get: unknown bridgetype bridge 0x%p",
> - ptr);
> - }
> + switch (pcibus_info->pbi_bridge_type) {
> + case PCIBR_BRIDGETYPE_TIOCP:
> + ret = __sn_readq_relaxed(&ptr->tio.cp_tflush);
> + break;
> + case PCIBR_BRIDGETYPE_PIC:
> + ret = __sn_readq_relaxed(&ptr->pic.p_wid_tflush);
> + break;
> + default:
> + panic("pcireg_tflush_get: unknown bridgetype bridge 0x%p",
> + ptr);
> }
>
> /* Read of the Target Flush should always return zero */
> @@ -96,24 +87,21 @@ u64 pcireg_tflush_get(struct pcibus_info *pcibus_info)
> /*
> * Interrupt Status Register Access -- Read Only 0000_0100
> */
> -u64 pcireg_intr_status_get(struct pcibus_info * pcibus_info)
> +u64 pcireg_intr_status_get(struct pcibus_info *pcibus_info)
> {
> union br_ptr __iomem *ptr = (union br_ptr __iomem *)pcibus_info->pbi_buscommon.bs_base;
> u64 ret = 0;
>
> - if (pcibus_info) {
> - switch (pcibus_info->pbi_bridge_type) {
> - case PCIBR_BRIDGETYPE_TIOCP:
> - ret = __sn_readq_relaxed(&ptr->tio.cp_int_status);
> - break;
> - case PCIBR_BRIDGETYPE_PIC:
> - ret = __sn_readq_relaxed(&ptr->pic.p_int_status);
> - break;
> - default:
> - panic
> - ("pcireg_intr_status_get: unknown bridgetype bridge 0x%p",
> - ptr);
> - }
> + switch (pcibus_info->pbi_bridge_type) {
> + case PCIBR_BRIDGETYPE_TIOCP:
> + ret = __sn_readq_relaxed(&ptr->tio.cp_int_status);
> + break;
> + case PCIBR_BRIDGETYPE_PIC:
> + ret = __sn_readq_relaxed(&ptr->pic.p_int_status);
> + break;
> + default:
> + panic("pcireg_intr_status_get: unknown bridgetype bridge 0x%p",
> + ptr);
> }
> return ret;
> }
> @@ -125,19 +113,16 @@ void pcireg_intr_enable_bit_clr(struct pcibus_info *pcibus_info, u64 bits)
> {
> union br_ptr __iomem *ptr = (union br_ptr __iomem *)pcibus_info->pbi_buscommon.bs_base;
>
> - if (pcibus_info) {
> - switch (pcibus_info->pbi_bridge_type) {
> - case PCIBR_BRIDGETYPE_TIOCP:
> - __sn_clrq_relaxed(&ptr->tio.cp_int_enable, bits);
> - break;
> - case PCIBR_BRIDGETYPE_PIC:
> - __sn_clrq_relaxed(&ptr->pic.p_int_enable, bits);
> - break;
> - default:
> - panic
> - ("pcireg_intr_enable_bit_clr: unknown bridgetype bridge 0x%p",
> - ptr);
> - }
> + switch (pcibus_info->pbi_bridge_type) {
> + case PCIBR_BRIDGETYPE_TIOCP:
> + __sn_clrq_relaxed(&ptr->tio.cp_int_enable, bits);
> + break;
> + case PCIBR_BRIDGETYPE_PIC:
> + __sn_clrq_relaxed(&ptr->pic.p_int_enable, bits);
> + break;
> + default:
> + panic("pcireg_intr_enable_bit_clr: unknown bridgetype bridge 0x%p",
> + ptr);
> }
> }
>
> @@ -145,19 +130,16 @@ void pcireg_intr_enable_bit_set(struct pcibus_info *pcibus_info, u64 bits)
> {
> union br_ptr __iomem *ptr = (union br_ptr __iomem *)pcibus_info->pbi_buscommon.bs_base;
>
> - if (pcibus_info) {
> - switch (pcibus_info->pbi_bridge_type) {
> - case PCIBR_BRIDGETYPE_TIOCP:
> - __sn_setq_relaxed(&ptr->tio.cp_int_enable, bits);
> - break;
> - case PCIBR_BRIDGETYPE_PIC:
> - __sn_setq_relaxed(&ptr->pic.p_int_enable, bits);
> - break;
> - default:
> - panic
> - ("pcireg_intr_enable_bit_set: unknown bridgetype bridge 0x%p",
> - ptr);
> - }
> + switch (pcibus_info->pbi_bridge_type) {
> + case PCIBR_BRIDGETYPE_TIOCP:
> + __sn_setq_relaxed(&ptr->tio.cp_int_enable, bits);
> + break;
> + case PCIBR_BRIDGETYPE_PIC:
> + __sn_setq_relaxed(&ptr->pic.p_int_enable, bits);
> + break;
> + default:
> + panic("pcireg_intr_enable_bit_set: unknown bridgetype bridge 0x%p",
> + ptr);
> }
> }
>
> @@ -169,25 +151,22 @@ void pcireg_intr_addr_addr_set(struct pcibus_info *pcibus_info, int int_n,
> {
> union br_ptr __iomem *ptr = (union br_ptr __iomem *)pcibus_info->pbi_buscommon.bs_base;
>
> - if (pcibus_info) {
> - switch (pcibus_info->pbi_bridge_type) {
> - case PCIBR_BRIDGETYPE_TIOCP:
> - __sn_clrq_relaxed(&ptr->tio.cp_int_addr[int_n],
> - TIOCP_HOST_INTR_ADDR);
> - __sn_setq_relaxed(&ptr->tio.cp_int_addr[int_n],
> - (addr & TIOCP_HOST_INTR_ADDR));
> - break;
> - case PCIBR_BRIDGETYPE_PIC:
> - __sn_clrq_relaxed(&ptr->pic.p_int_addr[int_n],
> - PIC_HOST_INTR_ADDR);
> - __sn_setq_relaxed(&ptr->pic.p_int_addr[int_n],
> - (addr & PIC_HOST_INTR_ADDR));
> - break;
> - default:
> - panic
> - ("pcireg_intr_addr_addr_get: unknown bridgetype bridge 0x%p",
> - ptr);
> - }
> + switch (pcibus_info->pbi_bridge_type) {
> + case PCIBR_BRIDGETYPE_TIOCP:
> + __sn_clrq_relaxed(&ptr->tio.cp_int_addr[int_n],
> + TIOCP_HOST_INTR_ADDR);
> + __sn_setq_relaxed(&ptr->tio.cp_int_addr[int_n],
> + (addr & TIOCP_HOST_INTR_ADDR));
> + break;
> + case PCIBR_BRIDGETYPE_PIC:
> + __sn_clrq_relaxed(&ptr->pic.p_int_addr[int_n],
> + PIC_HOST_INTR_ADDR);
> + __sn_setq_relaxed(&ptr->pic.p_int_addr[int_n],
> + (addr & PIC_HOST_INTR_ADDR));
> + break;
> + default:
> + panic("pcireg_intr_addr_addr_get: unknown bridgetype bridge 0x%p",
> + ptr);
> }
> }
>
> @@ -198,19 +177,16 @@ void pcireg_force_intr_set(struct pcibus_info *pcibus_info, int int_n)
> {
> union br_ptr __iomem *ptr = (union br_ptr __iomem *)pcibus_info->pbi_buscommon.bs_base;
>
> - if (pcibus_info) {
> - switch (pcibus_info->pbi_bridge_type) {
> - case PCIBR_BRIDGETYPE_TIOCP:
> - writeq(1, &ptr->tio.cp_force_pin[int_n]);
> - break;
> - case PCIBR_BRIDGETYPE_PIC:
> - writeq(1, &ptr->pic.p_force_pin[int_n]);
> - break;
> - default:
> - panic
> - ("pcireg_force_intr_set: unknown bridgetype bridge 0x%p",
> - ptr);
> - }
> + switch (pcibus_info->pbi_bridge_type) {
> + case PCIBR_BRIDGETYPE_TIOCP:
> + writeq(1, &ptr->tio.cp_force_pin[int_n]);
> + break;
> + case PCIBR_BRIDGETYPE_PIC:
> + writeq(1, &ptr->pic.p_force_pin[int_n]);
> + break;
> + default:
> + panic("pcireg_force_intr_set: unknown bridgetype bridge 0x%p",
> + ptr);
> }
> }
>
> @@ -222,21 +198,20 @@ u64 pcireg_wrb_flush_get(struct pcibus_info *pcibus_info, int device)
> union br_ptr __iomem *ptr = (union br_ptr __iomem *)pcibus_info->pbi_buscommon.bs_base;
> u64 ret = 0;
>
> - if (pcibus_info) {
> - switch (pcibus_info->pbi_bridge_type) {
> - case PCIBR_BRIDGETYPE_TIOCP:
> - ret =
> - __sn_readq_relaxed(&ptr->tio.cp_wr_req_buf[device]);
> - break;
> - case PCIBR_BRIDGETYPE_PIC:
> - ret =
> - __sn_readq_relaxed(&ptr->pic.p_wr_req_buf[device]);
> - break;
> - default:
> - panic("pcireg_wrb_flush_get: unknown bridgetype bridge 0x%p", ptr);
> - }
> -
> + switch (pcibus_info->pbi_bridge_type) {
> + case PCIBR_BRIDGETYPE_TIOCP:
> + ret =
> + __sn_readq_relaxed(&ptr->tio.cp_wr_req_buf[device]);
> + break;
> + case PCIBR_BRIDGETYPE_PIC:
> + ret =
> + __sn_readq_relaxed(&ptr->pic.p_wr_req_buf[device]);
> + break;
> + default:
> + panic("pcireg_wrb_flush_get: unknown bridgetype bridge 0x%p",
> + ptr);
> }
> +
> /* Read of the Write Buffer Flush should always return zero */
> return ret;
> }
> @@ -246,19 +221,16 @@ void pcireg_int_ate_set(struct pcibus_info *pcibus_info, int ate_index,
> {
> union br_ptr __iomem *ptr = (union br_ptr __iomem *)pcibus_info->pbi_buscommon.bs_base;
>
> - if (pcibus_info) {
> - switch (pcibus_info->pbi_bridge_type) {
> - case PCIBR_BRIDGETYPE_TIOCP:
> - writeq(val, &ptr->tio.cp_int_ate_ram[ate_index]);
> - break;
> - case PCIBR_BRIDGETYPE_PIC:
> - writeq(val, &ptr->pic.p_int_ate_ram[ate_index]);
> - break;
> - default:
> - panic
> - ("pcireg_int_ate_set: unknown bridgetype bridge 0x%p",
> - ptr);
> - }
> + switch (pcibus_info->pbi_bridge_type) {
> + case PCIBR_BRIDGETYPE_TIOCP:
> + writeq(val, &ptr->tio.cp_int_ate_ram[ate_index]);
> + break;
> + case PCIBR_BRIDGETYPE_PIC:
> + writeq(val, &ptr->pic.p_int_ate_ram[ate_index]);
> + break;
> + default:
> + panic("pcireg_int_ate_set: unknown bridgetype bridge 0x%p",
> + ptr);
> }
> }
>
> @@ -267,19 +239,16 @@ u64 __iomem *pcireg_int_ate_addr(struct pcibus_info *pcibus_info, int ate_index)
> union br_ptr __iomem *ptr = (union br_ptr __iomem *)pcibus_info->pbi_buscommon.bs_base;
> u64 __iomem *ret = NULL;
>
> - if (pcibus_info) {
> - switch (pcibus_info->pbi_bridge_type) {
> - case PCIBR_BRIDGETYPE_TIOCP:
> - ret = &ptr->tio.cp_int_ate_ram[ate_index];
> - break;
> - case PCIBR_BRIDGETYPE_PIC:
> - ret = &ptr->pic.p_int_ate_ram[ate_index];
> - break;
> - default:
> - panic
> - ("pcireg_int_ate_addr: unknown bridgetype bridge 0x%p",
> - ptr);
> - }
> + switch (pcibus_info->pbi_bridge_type) {
> + case PCIBR_BRIDGETYPE_TIOCP:
> + ret = &ptr->tio.cp_int_ate_ram[ate_index];
> + break;
> + case PCIBR_BRIDGETYPE_PIC:
> + ret = &ptr->pic.p_int_ate_ram[ate_index];
> + break;
> + default:
> + panic("pcireg_int_ate_addr: unknown bridgetype bridge 0x%p",
> + ptr);
> }
> return ret;
> }
> --
> 1.7.4.5
>
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