On Thu, Aug 19, 2021 at 10:33:43AM +0530, Lazar, Lijo wrote:

On 8/19/2021 5:29 AM, Kees Cook wrote:

quoted

On Wed, Aug 18, 2021 at 05:12:28PM +0530, Lazar, Lijo wrote:

quoted

On 8/18/2021 11:34 AM, Kees Cook wrote:

quoted

In preparation for FORTIFY_SOURCE performing compile-time and run-time
field bounds checking for memcpy(), memmove(), and memset(), avoid
intentionally writing across neighboring fields.

Use struct_group() in structs:
	struct atom_smc_dpm_info_v4_5
	struct atom_smc_dpm_info_v4_6
	struct atom_smc_dpm_info_v4_7
	struct atom_smc_dpm_info_v4_10
	PPTable_t
so the grouped members can be referenced together. This will allow
memcpy() and sizeof() to more easily reason about sizes, improve
readability, and avoid future warnings about writing beyond the end of
the first member.

"pahole" shows no size nor member offset changes to any structs.
"objdump -d" shows no object code changes.

Cc: "Christian König" <christian.koenig@amd.com>
Cc: "Pan, Xinhui" <redacted>
Cc: David Airlie <redacted>
Cc: Daniel Vetter <redacted>
Cc: Hawking Zhang <redacted>
Cc: Feifei Xu <redacted>
Cc: Lijo Lazar <redacted>
Cc: Likun Gao <redacted>
Cc: Jiawei Gu <redacted>
Cc: Evan Quan <redacted>
Cc: amd-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Kees Cook <redacted>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Link: https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Flkml%2FCADnq5_Npb8uYvd%2BR4UHgf-w8-cQj3JoODjviJR_Y9w9wqJ71mQ%40mail.gmail.com&amp;data=04%7C01%7Clijo.lazar%40amd.com%7C3861f20094074bf7328808d962a433f2%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637649279701053991%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=386LcfJJGfQfHsXBuK17LMqxJ2nFtGoj%2FUjoN2ZtJd0%3D&amp;reserved=0
---
   drivers/gpu/drm/amd/include/atomfirmware.h           |  9 ++++++++-
   .../gpu/drm/amd/pm/inc/smu11_driver_if_arcturus.h    |  3 ++-
   drivers/gpu/drm/amd/pm/inc/smu11_driver_if_navi10.h  |  3 ++-
   .../gpu/drm/amd/pm/inc/smu13_driver_if_aldebaran.h   |  3 ++-

Hi Kees,

Hi! Thanks for looking into this.

quoted

The headers which define these structs are firmware/VBIOS interfaces and are
picked directly from those components. There are difficulties in grouping
them to structs at the original source as that involves other component
changes.

So, can you help me understand this a bit more? It sounds like these are
generated headers, yes? I'd like to understand your constraints and
weight them against various benefits that could be achieved here.

The groupings I made do appear to be roughly documented already,
for example:

    struct   atom_common_table_header  table_header;
      // SECTION: BOARD PARAMETERS
+  struct_group(dpm_info,

Something emitted the "BOARD PARAMETERS" section heading as a comment,
so it likely also would know where it ends, yes? The good news here is
that for the dpm_info groups, they all end at the end of the existing
structs, see:
	struct atom_smc_dpm_info_v4_5
	struct atom_smc_dpm_info_v4_6
	struct atom_smc_dpm_info_v4_7
	struct atom_smc_dpm_info_v4_10

The matching regions in the PPTable_t structs are similarly marked with a
"BOARD PARAMETERS" section heading comment:

--- a/drivers/gpu/drm/amd/pm/inc/smu11_driver_if_arcturus.h
+++ b/drivers/gpu/drm/amd/pm/inc/smu11_driver_if_arcturus.h

@@ -643,6 +643,7 @@ typedef struct {
    // SECTION: BOARD PARAMETERS
    // SVI2 Board Parameters
+  struct_group(v4_6,
    uint16_t     MaxVoltageStepGfx; // In mV(Q2) Max voltage step that SMU will request. Multiple steps are taken if voltage change exceeds this value.
    uint16_t     MaxVoltageStepSoc; // In mV(Q2) Max voltage step that SMU will request. Multiple steps are taken if voltage change exceeds this value.

@@ -728,10 +729,10 @@ typedef struct {
    uint32_t     BoardVoltageCoeffB;    // decode by /1000
    uint32_t     BoardReserved[7];
+  );
    // Padding for MMHUB - do not modify this
    uint32_t     MmHubPadding[8]; // SMU internal use
-
  } PPTable_t;

Where they end seems known as well (the padding switches from a "Board"
to "MmHub" prefix at exactly the matching size).

So, given that these regions are already known by the export tool, how
about just updating the export tool to emit a struct there? I imagine
the problem with this would be the identifier churn needed, but that's
entirely mechanical.

However, I'm curious about another aspect of these regions: they are,
by definition, the same. Why isn't there a single struct describing
them already, given the existing redundancy? For example, look at the
member names: maxvoltagestepgfx vs MaxVoltageStepGfx. Why aren't these
the same? And then why aren't they described separately?

Fixing that would cut down on the redundancy here, and in the renaming,
you can fix the identifiers as well. It should be straight forward to
write a Coccinelle script to do this renaming for you after extracting
the structure.

quoted

The driver_if_* files updates are frequent and it is error prone to manually
group them each time we pick them for any update.

Why are these structs updated? It looks like they're specifically
versioned, and aren't expected to change (i.e. v4.5, v4.6, v4.10, etc).

quoted

Our usage of memcpy in this way is restricted only to a very few places.

True, there's 1 per PPTable_t duplication. With a proper struct, you
wouldn't even need a memcpy().

Instead of the existing:
                memcpy(smc_pptable->I2cControllers, smc_dpm_table_v4_7->I2cControllers,
                        sizeof(*smc_dpm_table_v4_7) - sizeof(smc_dpm_table_v4_7->table_header));

or my proposed:
                memcpy(&smc_pptable->v4, &smc_dpm_table_v4_7->dpm_info,
                       sizeof(smc_dpm_table_v4_7->dpm_info));

you could just have:
		smc_pptable->v4 = smc_dpm_table_v4_7->dpm_info;

since they'd be explicitly the same type.

That looks like a much cleaner solution to this. It greatly improves
readability, reduces the redundancy in the headers, and should be a
simple mechanical refactoring.

Oh my, I just noticed append_vbios_pptable() in
drivers/gpu/drm/amd/pm/powerplay/hwmgr/vega12_processpptables.c
which does an open-coded assignment of the entire PPTable_t, including
padding, and, apparently, the i2c address twice:

         ppsmc_pptable->Vr2_I2C_address = smc_dpm_table.Vr2_I2C_address;

         ppsmc_pptable->Vr2_I2C_address = smc_dpm_table.Vr2_I2C_address;

quoted

As another option - is it possible to have a helper function/macro like
memcpy_fortify() which takes the extra arguments and does the extra compile
time checks? We will use the helper whenever we have such kind of usage.

I'd rather avoid special cases just for this, especially when the code
here is already doing a couple things we try to avoid in the rest of
the kernel (i.e. open coded redundant struct contents, etc).

If something mechanically produced append_vbios_pptable() above, I bet
we can get rid of the memcpy()s entirely and save a lot of code doing a
member-to-member assignment.

What do you think?

Hi Kees,

Will give a background on why there are multiple headers and why it's
structured this way. That may help to better understand this arrangement.

This code is part of driver for AMD GPUs. These GPUs get to the consumers
through multiple channels - AMD designs a few boards with those, there are
add-in-board partners like ASRock, Sapphire etc. who take these ASICs and
design their own boards, and others like OEM vendors who have their own
design for boards in their laptops.

As you have noticed, this particular section in the structure carries
information categorized as 'BOARD PARAMETERS'. Since there are multiple
vendors designing their own boards, this gives the option to customize the
parameters based on their board design.

There are a few components in AMD GPUs which are interested in these board
parameters main ones being - Video BIOS (VBIOS) and power management
firmware (PMFW). There needs to be a single source where a vendor can input
the information and that is decided as VBIOS. VBIOS carries different data
tables which carry other information also (some of which are used by
driver), so this information is added as a separate data table in VBIOS. A
board vendor can customize the VBIOS build with this information.

The data tables (and some other interfaces with driver) carried by VBIOS are
published in this header - drivers/gpu/drm/amd/include/atomfirmware.h

I understand this to mean that this header is shared by other projects?

If that's true, what compilers are processing this header? (i.e. so I
can scope my suggestions to things that all the compilers will be able
to deal with.)

How are edits of this file managed "upstream" from the Linux kernel?

Why does it have strange indentations like this:

  uint8_t  ledpin0;
  uint8_t  ledpin1;
  uint8_t  ledpin2;
  uint8_t  padding8_4;

	uint8_t  pllgfxclkspreadenabled;
	uint8_t  pllgfxclkspreadpercent;
	uint16_t pllgfxclkspreadfreq;

  uint8_t uclkspreadenabled;
  uint8_t uclkspreadpercent;
  uint16_t uclkspreadfreq;

There are multiple families of AMD GPUs like Navi10, Arcturus, Aldebaran
etc. and the board specific details change with different families of GPUs.
However, VBIOS team publishes a common header file for these GPUs and any
difference in data tables (between GPU families) is maintained through a
versioning scheme. Thus there are different tables like
atom_smc_dpm_info_v4_5, atom_smc_dpm_info_v4_6 etc. which are relevant for a
particular family of GPUs.

With newer VBIOS versions and new GPU families, there could be changes in
the structs defined in atomfirmware.h and we pick the header accordingly.

As mentioned earlier, one other user of the board specific information is
power management firmware (PMFW). PMFW design is isolated from the actual
source of board information. In addition to board specific information, PMFW
needs some other info as well and driver is the one responsible for passing
this info to the firmware. PMFW gives an interface header to driver
providing the different struct formats which are used in driver<->PMFW
interactions. Unlike VBIOS, these interface headers are defined per family
of ASICs and those are smu11_driver_if_arcturus.h, smu11_driver_if_* etc.
(in short driver_if_* files). Like VBIOS,  with newer firmware versions,
there could be changes in the different structs defined in these headers and
we pick them accordingly.

Are these headers also shared between other projects?

What's needed to coordinate making these less redundant? (i.e. replacing
the "BOARD PARAMETERS" portion of PPTable_t with the associated
struct *_dpm_info_v* from atomfirmware.h?)

Driver acts the intermediary between actual source of board information
(VBIOS) and PMFW. So what is being done here is driver picks the board
information from VBIOS table, strips the VBIOS table header and passes it as
part of PPTable_t which defines all the information that is needed by PMFW
from driver for enabling dynamic power management.

In summary, these headers are not generated and not owned by driver. They
define the interfaces of two different components with driver, and are
consumed by those components themselves. A simple change to group the
information as a separate structure involves changes in multiple components
like VBIOS, PMFW, software used to build VBIOS, Windows driver etc.

In all practical cases, this code is harmless as these structs (in both
headers) are well defined for a specific family of GPUs. There is always a
reserve field defined with some extra bytes so that the size is not affected
if at all new fields need to be added.

It sounds like it's unlikely that the headers will be able to change? If
that's true, it seems like a good idea to mark those headers very
clearly at the top with details like you describe here. Maybe something
like:

/*
 * This header file is shared between VBIOS, Windows drivers, and Linux
 * drivers. Any changes need to be well justified and coordinated with
 * email@address...
 */

And in looking through these, I notice there's a typo in the Description:

    header file of general definitions for OS nd pre-OS video drivers

nd -> and

The patch now makes us to modify the headers for Linux through
script/manually whenever we pick them, and TBH that strips off the coherency
with the original source. The other option is field by field copy. Now we
use memcpy as a safe bet so that a new field added later taking some reserve
space is not missed even if we miss a header update.

How does this look as a work-around for now:

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu.h b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
index 96e895d6be35..4605934a4fb7 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu.h

@@ -1446,4 +1446,29 @@ static inline int amdgpu_in_reset(struct amdgpu_device *adev)
 {
 	return atomic_read(&adev->in_gpu_reset);
 }
+
+/**
+ * memcpy_trailing - Copy the end of one structure into the middle of another
+ *
+ * @dst: Pointer to destination struct
+ * @first_dst_member: The member name in @dst where the overwrite begins
+ * @last_dst_member: The member name in @dst where the overwrite ends after
+ * @src: Pointer to the source struct
+ * @first_src_member: The member name in @src where the copy begins
+ *
+ */
+#define memcpy_trailing(dst, first_dst_member, last_dst_member,		   \
+		        src, first_src_member)				   \
+({									   \
+	size_t __src_offset = offsetof(typeof(*(src)), first_src_member);  \
+	size_t __src_size = sizeof(*(src)) - __src_offset;		   \
+	size_t __dst_offset = offsetof(typeof(*(dst)), first_dst_member);  \
+	size_t __dst_size = offsetofend(typeof(*(dst)), last_dst_member) - \
+			    __dst_offset;				   \
+	BUILD_BUG_ON(__src_size != __dst_size);				   \
+	__builtin_memcpy((u8 *)(dst) + __dst_offset,			   \
+			 (u8 *)(src) + __src_offset,			   \
+			 __dst_size);					   \
+})
+
 #endif

diff --git a/drivers/gpu/drm/amd/pm/swsmu/smu11/arcturus_ppt.c b/drivers/gpu/drm/amd/pm/swsmu/smu11/arcturus_ppt.c
index 8ab58781ae13..1918e6232319 100644
--- a/drivers/gpu/drm/amd/pm/swsmu/smu11/arcturus_ppt.c
+++ b/drivers/gpu/drm/amd/pm/swsmu/smu11/arcturus_ppt.c

@@ -465,10 +465,8 @@ static int arcturus_append_powerplay_table(struct smu_context *smu)
 
 	if ((smc_dpm_table->table_header.format_revision == 4) &&
 	    (smc_dpm_table->table_header.content_revision == 6))
-		memcpy(&smc_pptable->MaxVoltageStepGfx,
-		       &smc_dpm_table->maxvoltagestepgfx,
-		       sizeof(*smc_dpm_table) - offsetof(struct atom_smc_dpm_info_v4_6, maxvoltagestepgfx));
-
+		memcpy_trailing(smc_pptable, MaxVoltageStepGfx, BoardReserved,
+				smc_dpm_table, maxvoltagestepgfx);
 	return 0;
 }
 

diff --git a/drivers/gpu/drm/amd/pm/swsmu/smu11/navi10_ppt.c b/drivers/gpu/drm/amd/pm/swsmu/smu11/navi10_ppt.c
index 2e5d3669652b..b738042e064d 100644
--- a/drivers/gpu/drm/amd/pm/swsmu/smu11/navi10_ppt.c
+++ b/drivers/gpu/drm/amd/pm/swsmu/smu11/navi10_ppt.c

@@ -431,16 +431,16 @@ static int navi10_append_powerplay_table(struct smu_context *smu)
 
 	switch (smc_dpm_table->table_header.content_revision) {
 	case 5: /* nv10 and nv14 */
-		memcpy(smc_pptable->I2cControllers, smc_dpm_table->I2cControllers,
-			sizeof(*smc_dpm_table) - sizeof(smc_dpm_table->table_header));
+		memcpy_trailing(smc_pptable, I2cControllers, BoardReserved,
+				smc_dpm_table, I2cControllers);
 		break;
 	case 7: /* nv12 */
 		ret = amdgpu_atombios_get_data_table(adev, index, NULL, NULL, NULL,
 					      (uint8_t **)&smc_dpm_table_v4_7);
 		if (ret)
 			return ret;
-		memcpy(smc_pptable->I2cControllers, smc_dpm_table_v4_7->I2cControllers,
-			sizeof(*smc_dpm_table_v4_7) - sizeof(smc_dpm_table_v4_7->table_header));
+		memcpy_trailing(smc_pptable, I2cControllers, BoardReserved,
+				smc_dpm_table_v4_7, I2cControllers);
 		break;
 	default:
 		dev_err(smu->adev->dev, "smc_dpm_info with unsupported content revision %d!\n",

diff --git a/drivers/gpu/drm/amd/pm/swsmu/smu13/aldebaran_ppt.c b/drivers/gpu/drm/amd/pm/swsmu/smu13/aldebaran_ppt.c
index c8eefacfdd37..a6fd7ee314a9 100644
--- a/drivers/gpu/drm/amd/pm/swsmu/smu13/aldebaran_ppt.c
+++ b/drivers/gpu/drm/amd/pm/swsmu/smu13/aldebaran_ppt.c

@@ -409,9 +409,8 @@ static int aldebaran_append_powerplay_table(struct smu_context *smu)
 
 	if ((smc_dpm_table->table_header.format_revision == 4) &&
 	    (smc_dpm_table->table_header.content_revision == 10))
-		memcpy(&smc_pptable->GfxMaxCurrent,
-		       &smc_dpm_table->GfxMaxCurrent,
-		       sizeof(*smc_dpm_table) - offsetof(struct atom_smc_dpm_info_v4_10, GfxMaxCurrent));
+		memcpy_trailing(smc_pptable, GfxMaxCurrent, reserved,
+				smc_dpm_table, GfxMaxCurrent);
 	return 0;
 }
 

-- 
Kees Cook