On 8/1/2018 8:56 AM, Eric Snowberg wrote:
Commit d2078d5adbe2 ("x86: EFI stub support for large memory maps")
added support for EFI memory maps larger than 128 entries. Following
allocation for this new buffer (within the exit_boot function calling
alloc_e820ext) another call to efi_get_memory_map was performed.
This took place before the final call to ExitBootServices (EBS) to
insure the memory map buffer was large enough since memory allocation
is not allowed after calling EBS.
Later this code was refactored and portions were added to
efi-stub-helper.c. The call to efi_get_memory_map did not remain after
calling alloc_e820ext. In a later patch, a new EFI_MMAP_NR_SLACK_SLOTS was
introduced to help give some headroom should the memory map grow after
the EBS is called. This does not alway provide enough space with large
memory maps.
It might be nice if you CC'd the authors of the changes you are "fixing"
so that they can chime in. I guess I'm lucky I noticed this on the
list. You should probably also have a "fixes tag".
Can you elaborate on the specific scenario where EFI_MMAP_NR_SLACK_CLOTS
is insufficient? What is the exact failure encountered?
This change will call efi_get_memory_map one final time before calling EBS,
ensuring there is enough room for the memory map buffer. The additional
headroom will be left alone for any memory change that may currently
be in flight between the final efi_get_memory_map call and EBS.
Uhh, I'm thinking this should be Nack'd.
This invalidates the entire point of the priv_func because now the
memory map may have changed after it was processed by priv_func, but the
mem map may not have changed between your added call and EBS. If that
happens, EBS will pass, and we'll go into linux with a corrupt mem map.
The mem map can still change between your added call and EBS, so you
haven't really done anything to address the existing race condition.
Signed-off-by: Eric Snowberg <eric.snowberg@xxxxxxxxxx>
---
drivers/firmware/efi/libstub/efi-stub-helper.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/drivers/firmware/efi/libstub/efi-stub-helper.c b/drivers/firmware/efi/libstub/efi-stub-helper.c
index b018436..3363b4e 100644
--- a/drivers/firmware/efi/libstub/efi-stub-helper.c
+++ b/drivers/firmware/efi/libstub/efi-stub-helper.c
@@ -845,6 +845,14 @@ efi_status_t efi_exit_boot_services(efi_system_table_t *sys_table_arg,
if (status != EFI_SUCCESS)
goto free_map;
+ /*
+ * priv_func could have allocated memory, thus call efi_get_memory_map
+ * one more time.
+ */
+ status = efi_get_memory_map(sys_table_arg, map);
+ if (status != EFI_SUCCESS)
+ goto fail;
+
status = efi_call_early(exit_boot_services, handle, *map->key_ptr);
if (status == EFI_INVALID_PARAMETER) {
--
Jeffrey Hugo
Qualcomm Datacenter Technologies as an affiliate of Qualcomm
Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.
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