Re: [PATCH] Fix devmem_is_allowed for below 1MB accesses for an efi machine
On 10/04/2012 01:07 PM, Randy Wright wrote: > > I wanted to mention in this context a patch RFC I posted yesterday as a > distinct thread which is visible as https://lkml.org/lkml/2012/10/3/589 > with the subject: [PATCH RFC] function probe_roms accessing improper > addresses on UEFI systems. > And it's equally as wrong. It has nothing to do with UEFI vs BIOS at all; this is rather a change in the classic behavior on x86 to return -1 on an impossible read rather than #MC. Normally I would say probe_roms() doesn't really make any sense in the EFI context anyway, but I believe there are systems which actually need to probe at least for the video ROM even when running under EFI (and I think there are storage devices which have parameter blocks in their ROMs with similar issues). Excluding reserved regions in general is a non-option, because on a lot of systems the ROMs that *do* need to be probed for are marked just RESERVED. One option would be to quirk it; obviously there is some piece of hardware which does cause this #MC and hopefully we could use that to detect that specific regions should be excluded; another option would be to trap the #MC during ROM probing. -hpa -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] Fix devmem_is_allowed for below 1MB accesses for an efi machine
On 10/02/2012 11:20 PM, Matthew Garrett wrote: > Oh, right, got you. In that case I think we potentially need a > finer-grained check on EFI platforms - the EFI memory map is kind enough > to tell us the difference between unusable regions and io regions, and > we could avoid access to the unusable ones. I wanted to mention in this context a patch RFC I posted yesterday as a distinct thread which is visible as https://lkml.org/lkml/2012/10/3/589 with the subject: [PATCH RFC] function probe_roms accessing improper addresses on UEFI systems. While the mechanism is different from Tmac's patch (because probe_roms runs early in boot, prior to resource structure initialization) the intent of the change is the same: to prevent a machine check resulting from access to inappropriate physical addresses. I will monitor both this thread as well as my own recent RFC posting since the underlying issues are common. -- Randy Wright+1-970-898-0998 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] Fix devmem_is_allowed for below 1MB accesses for an efi machine
On 10/02/2012 11:20 PM, Matthew Garrett wrote: Oh, right, got you. In that case I think we potentially need a finer-grained check on EFI platforms - the EFI memory map is kind enough to tell us the difference between unusable regions and io regions, and we could avoid access to the unusable ones. I wanted to mention in this context a patch RFC I posted yesterday as a distinct thread which is visible as https://lkml.org/lkml/2012/10/3/589 with the subject: [PATCH RFC] function probe_roms accessing improper addresses on UEFI systems. While the mechanism is different from Tmac's patch (because probe_roms runs early in boot, prior to resource structure initialization) the intent of the change is the same: to prevent a machine check resulting from access to inappropriate physical addresses. I will monitor both this thread as well as my own recent RFC posting since the underlying issues are common. -- Randy Wrightrwri...@hp.com+1-970-898-0998 -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] Fix devmem_is_allowed for below 1MB accesses for an efi machine
On 10/04/2012 01:07 PM, Randy Wright wrote: I wanted to mention in this context a patch RFC I posted yesterday as a distinct thread which is visible as https://lkml.org/lkml/2012/10/3/589 with the subject: [PATCH RFC] function probe_roms accessing improper addresses on UEFI systems. And it's equally as wrong. It has nothing to do with UEFI vs BIOS at all; this is rather a change in the classic behavior on x86 to return -1 on an impossible read rather than #MC. Normally I would say probe_roms() doesn't really make any sense in the EFI context anyway, but I believe there are systems which actually need to probe at least for the video ROM even when running under EFI (and I think there are storage devices which have parameter blocks in their ROMs with similar issues). Excluding reserved regions in general is a non-option, because on a lot of systems the ROMs that *do* need to be probed for are marked just RESERVED. One option would be to quirk it; obviously there is some piece of hardware which does cause this #MC and hopefully we could use that to detect that specific regions should be excluded; another option would be to trap the #MC during ROM probing. -hpa -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] Fix devmem_is_allowed for below 1MB accesses for an efi machine
On 10/02/2012 10:28 PM, Matthew Garrett wrote:
> On Tue, Oct 02, 2012 at 11:13:17PM -0600, Thavatchai Makphaibulchoke wrote:
>
>> Sounds like a better solution is to allow accesses to only I/O regions
>> presented in the EFI memory map for physical addresses below 1 MB.
>
> That won't work - unfortunately we do still need the low region to be
> available for X because some platforms expect us to use int10 even on
> EFI (yes, yes, I know). Do you have a copy of the EFI memory map for a
> system that's broken with the current code?
>
I honestly think this calls for a quirk, or more likely, no action at
all ("don't do that, then.")
-hpa
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] Fix devmem_is_allowed for below 1MB accesses for an efi machine
On Tue, Oct 02, 2012 at 11:13:17PM -0600, Thavatchai Makphaibulchoke wrote: > Sounds like a better solution is to allow accesses to only I/O regions > presented in the EFI memory map for physical addresses below 1 MB. That won't work - unfortunately we do still need the low region to be available for X because some platforms expect us to use int10 even on EFI (yes, yes, I know). Do you have a copy of the EFI memory map for a system that's broken with the current code? -- Matthew Garrett | mj...@srcf.ucam.org -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] Fix devmem_is_allowed for below 1MB accesses for an efi machine
On 10/02/2012 10:15 PM, Matthew Garrett wrote: > On Tue, Oct 02, 2012 at 09:44:16PM -0700, H. Peter Anvin wrote: > >> We *always* expose the I/O regions to /dev/mem. That is what /dev/mem >> *does*. The above is an exception (which is really obsolete, too: we >> should simply disallow access to anything which is treated as system >> RAM, which doesn't include the BIOS regions in question; the only reason >> we don't is that some versions of X take a checksum of the RAM in the >> first megabyte as some kind of idiotic random seed.) > > Oh, right, got you. In that case I think we potentially need a > finer-grained check on EFI platforms - the EFI memory map is kind enough > to tell us the difference between unusable regions and io regions, and > we could avoid access to the unusable ones. > Well, we have the same in BIOS space with "reserved" regions. The problem is that they are actually I/O regions as far as programs like X, dmidecode and so on. -hpa -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] Fix devmem_is_allowed for below 1MB accesses for an efi machine
Thank you both for the comments. Sounds like a better solution is to allow accesses to only I/O regions presented in the EFI memory map for physical addresses below 1 MB. Do we need to worry about the X checksum in the first MB on an EFI system? Thanks, Mak. On 10/02/2012 11:15 PM, Matthew Garrett wrote: > On Tue, Oct 02, 2012 at 09:44:16PM -0700, H. Peter Anvin wrote: > >> We *always* expose the I/O regions to /dev/mem. That is what /dev/mem >> *does*. The above is an exception (which is really obsolete, too: we >> should simply disallow access to anything which is treated as system >> RAM, which doesn't include the BIOS regions in question; the only reason >> we don't is that some versions of X take a checksum of the RAM in the >> first megabyte as some kind of idiotic random seed.) > > Oh, right, got you. In that case I think we potentially need a > finer-grained check on EFI platforms - the EFI memory map is kind enough > to tell us the difference between unusable regions and io regions, and > we could avoid access to the unusable ones. > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] Fix devmem_is_allowed for below 1MB accesses for an efi machine
On Tue, Oct 02, 2012 at 09:44:16PM -0700, H. Peter Anvin wrote: > We *always* expose the I/O regions to /dev/mem. That is what /dev/mem > *does*. The above is an exception (which is really obsolete, too: we > should simply disallow access to anything which is treated as system > RAM, which doesn't include the BIOS regions in question; the only reason > we don't is that some versions of X take a checksum of the RAM in the > first megabyte as some kind of idiotic random seed.) Oh, right, got you. In that case I think we potentially need a finer-grained check on EFI platforms - the EFI memory map is kind enough to tell us the difference between unusable regions and io regions, and we could avoid access to the unusable ones. -- Matthew Garrett | mj...@srcf.ucam.org -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] Fix devmem_is_allowed for below 1MB accesses for an efi machine
On 10/02/2012 09:31 PM, Matthew Garrett wrote: > On Tue, Oct 02, 2012 at 02:50:09PM -0700, H. Peter Anvin wrote: > >> That sounds like exactly the opposite of normal /dev/mem behavior... we >> allow access to non-memory resources (which really could do anything if >> misused), but not memory. > > From arch/x86/mm/init.c: > > * On x86, access has to be given to the first megabyte of ram because that > area > * contains bios code and data regions used by X and dosemu and similar apps. > > Limiting this to just RAM would be safer than it currently is. I'm not > convinced that there's any good reason to allow *any* access down there > for EFI systems, though. > Sorry, fail. We *always* expose the I/O regions to /dev/mem. That is what /dev/mem *does*. The above is an exception (which is really obsolete, too: we should simply disallow access to anything which is treated as system RAM, which doesn't include the BIOS regions in question; the only reason we don't is that some versions of X take a checksum of the RAM in the first megabyte as some kind of idiotic random seed.) -hpa -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] Fix devmem_is_allowed for below 1MB accesses for an efi machine
On Tue, Oct 02, 2012 at 02:50:09PM -0700, H. Peter Anvin wrote: > That sounds like exactly the opposite of normal /dev/mem behavior... we > allow access to non-memory resources (which really could do anything if > misused), but not memory. >From arch/x86/mm/init.c: * On x86, access has to be given to the first megabyte of ram because that area * contains bios code and data regions used by X and dosemu and similar apps. Limiting this to just RAM would be safer than it currently is. I'm not convinced that there's any good reason to allow *any* access down there for EFI systems, though. -- Matthew Garrett | mj...@srcf.ucam.org -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] Fix devmem_is_allowed for below 1MB accesses for an efi machine
On 10/02/2012 02:32 PM, T Makphaibulchoke wrote: > Changing devmem_is_allowed so that on an EFI machine, access to physical > address below 1 MB is allowed only to physical pages that are valid in > the EFI memory map. This prevents the possibility of an MCE due to > accessing an invalid physical address. What? That sounds like exactly the opposite of normal /dev/mem behavior... we allow access to non-memory resources (which really could do anything if misused), but not memory. You seem like you're flipping it on its head. -hpa -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] Fix devmem_is_allowed for below 1MB accesses for an efi machine
On 10/02/2012 02:32 PM, T Makphaibulchoke wrote: Changing devmem_is_allowed so that on an EFI machine, access to physical address below 1 MB is allowed only to physical pages that are valid in the EFI memory map. This prevents the possibility of an MCE due to accessing an invalid physical address. What? That sounds like exactly the opposite of normal /dev/mem behavior... we allow access to non-memory resources (which really could do anything if misused), but not memory. You seem like you're flipping it on its head. -hpa -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] Fix devmem_is_allowed for below 1MB accesses for an efi machine
On Tue, Oct 02, 2012 at 02:50:09PM -0700, H. Peter Anvin wrote: That sounds like exactly the opposite of normal /dev/mem behavior... we allow access to non-memory resources (which really could do anything if misused), but not memory. From arch/x86/mm/init.c: * On x86, access has to be given to the first megabyte of ram because that area * contains bios code and data regions used by X and dosemu and similar apps. Limiting this to just RAM would be safer than it currently is. I'm not convinced that there's any good reason to allow *any* access down there for EFI systems, though. -- Matthew Garrett | mj...@srcf.ucam.org -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] Fix devmem_is_allowed for below 1MB accesses for an efi machine
On 10/02/2012 09:31 PM, Matthew Garrett wrote: On Tue, Oct 02, 2012 at 02:50:09PM -0700, H. Peter Anvin wrote: That sounds like exactly the opposite of normal /dev/mem behavior... we allow access to non-memory resources (which really could do anything if misused), but not memory. From arch/x86/mm/init.c: * On x86, access has to be given to the first megabyte of ram because that area * contains bios code and data regions used by X and dosemu and similar apps. Limiting this to just RAM would be safer than it currently is. I'm not convinced that there's any good reason to allow *any* access down there for EFI systems, though. Sorry, fail. We *always* expose the I/O regions to /dev/mem. That is what /dev/mem *does*. The above is an exception (which is really obsolete, too: we should simply disallow access to anything which is treated as system RAM, which doesn't include the BIOS regions in question; the only reason we don't is that some versions of X take a checksum of the RAM in the first megabyte as some kind of idiotic random seed.) -hpa -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] Fix devmem_is_allowed for below 1MB accesses for an efi machine
On Tue, Oct 02, 2012 at 09:44:16PM -0700, H. Peter Anvin wrote: We *always* expose the I/O regions to /dev/mem. That is what /dev/mem *does*. The above is an exception (which is really obsolete, too: we should simply disallow access to anything which is treated as system RAM, which doesn't include the BIOS regions in question; the only reason we don't is that some versions of X take a checksum of the RAM in the first megabyte as some kind of idiotic random seed.) Oh, right, got you. In that case I think we potentially need a finer-grained check on EFI platforms - the EFI memory map is kind enough to tell us the difference between unusable regions and io regions, and we could avoid access to the unusable ones. -- Matthew Garrett | mj...@srcf.ucam.org -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] Fix devmem_is_allowed for below 1MB accesses for an efi machine
Thank you both for the comments. Sounds like a better solution is to allow accesses to only I/O regions presented in the EFI memory map for physical addresses below 1 MB. Do we need to worry about the X checksum in the first MB on an EFI system? Thanks, Mak. On 10/02/2012 11:15 PM, Matthew Garrett wrote: On Tue, Oct 02, 2012 at 09:44:16PM -0700, H. Peter Anvin wrote: We *always* expose the I/O regions to /dev/mem. That is what /dev/mem *does*. The above is an exception (which is really obsolete, too: we should simply disallow access to anything which is treated as system RAM, which doesn't include the BIOS regions in question; the only reason we don't is that some versions of X take a checksum of the RAM in the first megabyte as some kind of idiotic random seed.) Oh, right, got you. In that case I think we potentially need a finer-grained check on EFI platforms - the EFI memory map is kind enough to tell us the difference between unusable regions and io regions, and we could avoid access to the unusable ones. -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] Fix devmem_is_allowed for below 1MB accesses for an efi machine
On 10/02/2012 10:15 PM, Matthew Garrett wrote: On Tue, Oct 02, 2012 at 09:44:16PM -0700, H. Peter Anvin wrote: We *always* expose the I/O regions to /dev/mem. That is what /dev/mem *does*. The above is an exception (which is really obsolete, too: we should simply disallow access to anything which is treated as system RAM, which doesn't include the BIOS regions in question; the only reason we don't is that some versions of X take a checksum of the RAM in the first megabyte as some kind of idiotic random seed.) Oh, right, got you. In that case I think we potentially need a finer-grained check on EFI platforms - the EFI memory map is kind enough to tell us the difference between unusable regions and io regions, and we could avoid access to the unusable ones. Well, we have the same in BIOS space with reserved regions. The problem is that they are actually I/O regions as far as programs like X, dmidecode and so on. -hpa -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] Fix devmem_is_allowed for below 1MB accesses for an efi machine
On Tue, Oct 02, 2012 at 11:13:17PM -0600, Thavatchai Makphaibulchoke wrote: Sounds like a better solution is to allow accesses to only I/O regions presented in the EFI memory map for physical addresses below 1 MB. That won't work - unfortunately we do still need the low region to be available for X because some platforms expect us to use int10 even on EFI (yes, yes, I know). Do you have a copy of the EFI memory map for a system that's broken with the current code? -- Matthew Garrett | mj...@srcf.ucam.org -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] Fix devmem_is_allowed for below 1MB accesses for an efi machine
On 10/02/2012 10:28 PM, Matthew Garrett wrote: On Tue, Oct 02, 2012 at 11:13:17PM -0600, Thavatchai Makphaibulchoke wrote: Sounds like a better solution is to allow accesses to only I/O regions presented in the EFI memory map for physical addresses below 1 MB. That won't work - unfortunately we do still need the low region to be available for X because some platforms expect us to use int10 even on EFI (yes, yes, I know). Do you have a copy of the EFI memory map for a system that's broken with the current code? I honestly think this calls for a quirk, or more likely, no action at all (don't do that, then.) -hpa -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
